It was necessary, therefore, to find some method that was more generally

applicable. With this object Koch himself began to study the blood serum

of animals that had recovered spontaneously from rinderpest. He was able

to assure not only himself, but several other observers, that this serum

was capable of rendering normal animals into which it is injected

refractory. Bordet and Danysz, who studied rinderpest in the Transvaal

in 1897, made many experiments in this direction and devised a method

which gave good results in practice. But it was left to Kolle and Turner

to work out a method at once simple and easily applied, one which soon

came into general use. This method is known by the name of “simultaneous

vaccinations.” It consists in the injection of a protective serum

simultaneously with the virulent blood. To prepare the former the

authors just mentioned made use of animals that had recovered

spontaneously from rinderpest or of Bovidae that had been immunised by

bile or by some other method. It was recognised that the protective

power of the serum of animals that have recovered is very small and

cannot confer immunity on normal animals, except when injected in large

doses. Kolle and Turner showed that if Bovidae that have recovered

spontaneously are injected with very large quantities of virulent blood

coming from animals fatally attacked, the protective power of the serum

of the former is markedly increased and a serum is obtained which is

active in small doses and which gives good results in practice. This

serum may be kept for a long time by the addition of a small quantity of

carbolic acid. The immunity conferred by this serum upon normal animals

is immediate, but of short duration; it is completed by making a

simultaneous injection of virulent blood; we thus obtain a double

immunity, one part immediate, the other permanent; to get this result,

however, the serum must not be mixed with the virulent blood, for when

this is done the immunity conferred is trifling or _nil_. On the other

hand, it is complete and persists for several months when the protective

serum is injected separately on one side of the body and the virulent

blood on the other.

Kolle and Turner had to defend their method against many ill-founded

objections and attacks, but they succeeded in getting it accepted, not

only in Cape Colony but also in many other parts of Africa, and in many

countries in Europe and in Asia. In 1898 it was decided at a conference

which met in Cape Town to use the method of simultaneous vaccinations to

the exclusion of all others. This method has since been applied on a

very large scale and it was not long before favourable results were

obtained. The same method has proved to be very successful with Nicolle

and Adil Bey[783] of Constantinople, who now prepare large quantities of

the antirinderpest serum, and combat this disease with great success in

the Ottoman empire. Yersin[784] adopted the same method to fight the

cattle plague in Indo-China, where it causes great ravages, especially

among buffaloes. His Institute at Nha-Trang has become a centre for the

preparation of the specific serum, which he distributes over a vast

territory. In the East Indies the simultaneous method has been applied

by Rogers[785]. In Russia, where rinderpest is endemic in many regions,

the Institute of Experimental Medicine at St Petersburg furnishes the

serum destined to prevent the propagation of this epizootic

disease[786].

In a few years this method of simultaneous vaccination has been extended

to all the countries ravaged by rinderpest and has already rendered

immense services to agriculture.

[Sidenote: [491]]

V. _Anti-anthrax vaccinations._ In the first four sections of this

Chapter we have brought together the methods which have as their basis

the vaccination by viruses whose nature is as yet unknown. Since we

cannot obtain them by artificial culture, we have to introduce them with

animal fluids:—either the contents of vaccinal or clavelar pustules, or

matter from rabic nervous centres, or again the blood of animals

attacked by rinderpest. In the case last mentioned, in order to prevent

the too serious effect of the injection of the virus, it is combined

with a simultaneous injection of protective serum.

[Sidenote: [492]]

In the case of the vaccinations against anthrax we pass to the group of

viruses whose organised nature is well known and which can be injected

in pure culture grown on artificially prepared media. This method

constitutes one of Pasteur’s most brilliant discoveries, made in

collaboration with Chamberland and Roux. Before they had found a

satisfactory method of vaccinating against anthrax these observers had

to solve the problem in connection with a less complicated and less

difficult case. From the first, in his studies on pathogenic

micro-organisms, Pasteur had devoted his attention to finding a means of

communicating immunity against these parasites. With the aid of

Chamberland and Roux he was not long in discovering a method by which it

was possible to attenuate the virulence of the micro-organism of fowl

cholera and to vaccinate fowls against this terrible disease by

inoculating them with this attenuated micro-organism. Guided by these

results Pasteur, Chamberland and Roux set to work to find the vaccine

against anthrax; they were soon confronted by a serious obstacle in the

formation of spores which prevented the attenuation of the bacilli. This

obstacle they overcame by submitting cultures of the bacillus to a

temperature of 42°·5 C. Under this condition spores do not develop, and

the bacilli become attenuated at the end of a longer or shorter period.

Although in possession of these attenuated viruses, it still needed very

laborious investigations to adapt them to the vaccination of various

species of animals susceptible to anthrax, especially sheep. In this

they were also successful, and in 1881, over 20 years ago, Pasteur and

his collaborators demonstrated the efficacy of their method on a large

number of animals. This demonstration was made at Pouilly-le-Fort before

a large commission. We may affirm that this celebrated experiment opened

a new path to science and to the practice of vaccination. It was

performed on 50 sheep, half of which were vaccinated twice with twelve

days’ interval, the other 25 sheep serving as control animals. Fourteen

days after the vaccination by the second vaccine all the 50 sheep were

subjected to a test inoculation of a very strong anthrax virus. Two days

later the vaccinated animals remained unaffected, whilst the control

animals had all succumbed to anthrax.

Similar experiments, undertaken in France, Hungary, Germany, Russia and

elsewhere, confirmed the efficacy of anthrax vaccinations and led to

their extension into all the countries where bacterial anthrax was rife.

From the year 1881 the method came into regular use, and before the end

of that year there had been vaccinated, in France alone, 62,000 sheep

and 6,000 Bovidae. Since these first attempts, made on a large scale,

gave such good results, the anti-anthrax practice was not long in

spreading through France, then into Hungary and several other European

countries. Later, it extended into other continents, especially into

South America (Argentina)[787] and Australia. Vaccinations against

anthrax were also applied to horses with the same good results[788].

In France the anti-anthrax vaccines are prepared at and sent out from

the Pasteur Institute of Paris. These vaccines consist of broth cultures

of attenuated bacilli, of which the weakest, the first vaccine, is fatal

to the mouse and small guinea-pigs. The bacilli of the second vaccine

are less attenuated, and are capable of killing not only adult

guinea-pigs but even a certain number of rabbits, when inoculated

subcutaneously. The two vaccines are races of the anthrax bacillus,

capable of producing spores which present the same degree of virulence

as the filamentous bacilli which gave them birth.

The anti-anthrax vaccines are sent out in tubes containing the quantity

necessary for the vaccination of a large number of animals. The

vaccinations are made especially in spring in order that the animals may

be protected during the hot season, which is usually more favourable to

the development of anthrax epidemics.

[Sidenote: [493]]

In the sheep the vaccines are injected below the skin on the inner

aspect of the thigh. One-eighth of a c.c. of the first vaccine is

injected with a somewhat modified Pravaz syringe. Twelve or fifteen days

later a similar injection is made on the opposite side with the second

vaccine. In the Bovidae the vaccines are injected behind the shoulders,

where the skin is thinnest. In the horse the injections must be made on

the sides of the neck and shoulders. In large mammals double the amount

(¼th of a c.c.) of each vaccine is injected.

The tubes of vaccine, once opened, should not be employed a second time.

Care must be taken to use the whole of their contents at one series of

vaccinations.

The vaccinal injections produce tumefaction at the point of inoculation

and are followed by a slight rise of temperature. But these symptoms are

of little importance and soon disappear. Serious complications and fatal

results from the vaccinations are very rare. The loss due to these

accidents is estimated at one-half per cent. in sheep and a quarter per

cent. in the Bovidae.

The refractory condition resulting from the vaccination requires for its

development a period of about a fortnight. The immunity is then very

substantial and lasts for a fairly long time. According to Chamberland

60% of the sheep retain their immunity a year after they have been

vaccinated. But as a great number of animals then become susceptible, it

is usual to revaccinate annually.

According to the statistics furnished by the vaccine department of the

Pasteur Institute there have been vaccinated, up to the 1st of January

1900, a total of 4,971,494 sheep, and 708,980 cattle. Abroad the

corresponding figures are 3,831,948 and 1,869,445. Altogether, the

number of animals vaccinated amounted to 11,381,867, of which 3,626,206

have been treated with the vaccine furnished by the Budapest Laboratory.

The results of the anti-anthrax vaccinations were found to be so

favourable that it was unnecessary to introduce any improvements in

technique. Attempts have certainly been made to prepare anti-anthrax

serums, and these have been successful, but up to the present such

serums have not been introduced into practice.

[Sidenote: [494]]

VI. _Vaccinations against symptomatic anthrax._ Symptomatic anthrax,

which is often confounded with true anthrax, is set up, as demonstrated

by Arloing, Cornevin, and Thomas, by a specific anaerobic micro-organism

to which has been given the name of _Bacillus chauvaei_. Immediately

after the discovery of the attenuation of viruses and of vaccines

against fowl cholera, the three observers above mentioned tried to apply

it to symptomatic anthrax. Finally they devised a method which was soon

adopted in practice, and which, for nearly twenty years, has been used

in the vaccination of the Bovidae in countries where symptomatic anthrax

is most prevalent. This is especially the case in mountainous districts,

such as Switzerland, the Bavarian Alps, the Dauphiné, L’Auvergne, etc.

Arloing, Cornevin, and Thomas[789] prepare two vaccines against

symptomatic anthrax by a method very different from that used in the

preparation of the Pasteurian anti-anthrax vaccines. They take the virus

from the muscles invaded by the micro-organism; they triturate a piece

of the tumefied muscle in a mortar, adding to it a few drops of water.

The mixture is filtered through muslin and the fluid dried at 37° C.; a

virulent brown powder is thus obtained. In the preparation of the

vaccines a portion of this powder is mixed with water and subjected to a

temperature of 100°–104° C. for seven hours. Another portion is heated

during the same number of hours to 90°–94° C. only. This latter forms

the second vaccine whilst the first portion constitutes the first.

In practice the two vaccinal powders are dissolved in cooled boiled

water and are introduced into the subcutaneous tissue of the animals

that it is wished to immunise. The second vaccine should be injected 8

to 12 days after the first. The vaccines are usually tolerated very well

by the Bovidae and confer upon them a definite and permanent immunity.

In spite of certain drawbacks this method, known as the “Lyons method,”

has proved to be a very serviceable one and is retained as the best

devised up to the present. Its efficacy is proved by the fact that in

the period from 1884 to 1895 in 400,000 vaccinated animals the mortality

has only been 1 per 1,000. Arloing, Cornevin, and Thomas thought that

raising the virus to a high temperature brought about a real

attenuation.

[Sidenote: [495]]

Leclainche and Vallée[790], who have recently returned to the study of

this question, have shown that this view cannot be maintained. In

reality the spores, after being heated to 90°–104° C., gave rise to

bacilli endowed with their normal and complete virulence. But the

heating in the preparation of the Lyons vaccines destroys the toxin

manufactured by the _Bacillus chauvaei_, with the result, that the

spores now become the prey of phagocytes: it is for this reason and for

this reason alone that the inoculation of these vaccines is so well

tolerated. All the spores of the vaccinal powder are not eaten by the

phagocytes: those which are found in the centre of solid particles of

the powder offer a prolonged resistance to the action of the cells, and

some of them germinating produce bacilli and give rise to a mild disease

capable of conferring immunity. The germination of these spores is

further facilitated by the presence of foreign micro-organisms in the

vaccinal powders; these organisms help to interfere with the

phagocytosis of the spores of symptomatic anthrax.

In the course of their researches, Leclainche and Vallée demonstrated

that it is easy to vaccinate animals susceptible to anthrax and to

confer on them a substantial immunity by means of a single protective

injection of a pure culture of _Bacillus chauvaei_. For this purpose

they use cultures grown in broth made from the pig’s stomach (“bouillon

de panse” or Martin’s broth) which they heat for 2 hours at 70° C. The

cultures, so treated and injected in quantities of 1 to 2 c.c. into

Bovidae, induce in them an immediate immunity. These authors are

persuaded that the vaccination by this method might be used on a large

scale with certain advantages over the method at present in use. A

single injection, instead of two, involves a great economy, and the

injection of pure vaccinal cultures obviates the accidents caused by the

foreign organisms which are found mixed with the Lyons vaccine.

On the other hand, Leclainche and Vallée think that vaccination by

serums has no future in the fight against symptomatic anthrax and should

only be used in exceptional cases.

It is evident that the Lyons method is capable of being improved and

some day may be replaced by another. Still it must be remembered that it

has already preserved a very great number of animals from certain death

by symptomatic anthrax.

[Sidenote: [496]]

VII. _Vaccinations against swine erysipelas._ Swine erysipelas is a

disease widely distributed in nearly all countries where the breeding of

pigs is carried on on a large scale. It is a very fatal disease, and it

is estimated that in France alone at least 100,000 pigs of the value of

more than five million francs succumb to it annually. Unfortunately

swine erysipelas is often confounded by breeders with other epizootic

diseases, especially pneumo-enteritis of the pig. This confusion has

often resulted in large losses to agriculture.

Soon after the vaccinations against anthrax became a part of veterinary

practice, Pasteur[791], assisted by Thuillier, took up the study of

swine erysipelas which was causing great ravages in the department of

Vaucluse. They were not long in discovering that the true cause of the

disease was a very small bacillus capable of growing in pure culture in

nutrient broth. Guided by his former investigations, Pasteur with his

collaborator undertook minute researches into the reinforcement and

attenuation of the virulence of the bacillus of swine erysipelas which

led them to the elaboration of a method of vaccination capable of

conferring on pigs a high degree of protection against the disease.

Following the line of the anthrax vaccinations, Pasteur and Thuillier

prepared two vaccines against the erysipelas, the first more attenuated

than the second. The bacilli of these two vaccines were cultivated in

broth and sent out in tubes similar to those employed in the

distribution of the anthrax vaccines.

The vaccines are in themselves innocuous and are capable of

communicating to the inoculated pig an immunity sufficiently durable to

be of real service. Young pigs being less susceptible to the erysipelas

than are the adults, it is generally preferred to vaccinate young pigs

of from two to four months. The vaccination is done at two separate

times. The first vaccine, in a dose of one-eighth of a cubic centimetre,

is inoculated subcutaneously on the inner aspect of the right thigh; the

second vaccine is inoculated in the same way, 12 or 15 days later, into

the left thigh. The immunity that follows these vaccinations is not

fully established until the end of the second week.

[Sidenote: [497]]

In spite of the many advantages of the Pasteurian method the

vaccinations against swine erysipelas have not spread so much as one

might have expected; and they have found a general application abroad

rather than in France. It is only necessary to cast a glance at the

statistics to be convinced of this. From the date of the introduction of

the Pasteurian vaccinations in 1884 up to the 1st January, 1900, there

had been vaccinated in France in all 428,746 pigs, whilst abroad, where

the vaccinations were introduced some years later, the number of pigs

vaccinated was 4,819,387. Of this number the great majority (4,194,191)

had been treated in Hungary. The losses amongst the vaccinated animals

were insignificant (1·68%) when compared with an average mortality of

20% amongst unvaccinated pigs.

This limited extension of the vaccination of pigs in France arises from

various causes. In many countries the breeding is on too small a scale

to allow of the intervention of the veterinarian and of the expenses

which the vaccinations involve. On the other hand, it cannot be denied

that the Pasteurian method presents certain drawbacks in practice. The

living, although attenuated, bacilli introduced may sometimes serve as

centres of infection, especially in cases, rare no doubt, where the

vaccinated animal contracts a chronic form of the disease. The

Pasteurian vaccines must, therefore, be avoided in districts where the

erysipelas has not yet appeared. Their application in countries already

infected presents the further drawback that the immunity requires for

its establishment a fairly long time, sufficiently long to permit the

micro-organism to kill a large number of pigs before the vaccines have

conferred any immunity upon them.

[Sidenote: [498]]

It is natural that, under such conditions, an attempt has been made to

replace the Pasteurian method by some other method less risky. Hence,

since the discovery of the principle of sero-therapy several

investigators have sought to apply it to swine erysipelas. Emmerich and

Mastbaum[792] were the first to demonstrate that the blood of rabbits,

immunised with the bacilli of this disease, acquire a very marked

protective power. They have even attempted to construct from the results

of their researches methods which might be applied practically. It is

especially however to Lorenz[793], a Darmstadt veterinarian, that we owe

the first practical application of this method. He prepared protective

serums by injecting erysipelas bacilli into rabbits and pigs, and

demonstrated that the inoculation of these serums, when combined with

that of the living bacilli, conferred upon pigs a sufficient immunity

and one that was set up immediately after the introduction of the serum.

According to Lorenz’s method it is first necessary to give a protective

injection of serum; some days (3–5) afterwards this is followed by an

inoculation of living bacilli coming from the attenuated erysipelas

known in Germany under the name of “Backsteinblattern.” About two weeks

later a further injection of the same bacilli, but in double quantity,

is given. This method, therefore, involves three vaccinal injections as

against two in the Pasteurian method. It is consequently dearer than the

latter, but, as it presents certain undeniable advantages, an attempt

was made to introduce it into veterinary practice. But being much more

complicated endeavours were made to simplify it. Voges and Schütz, by

methods which have remained secret, soon obtained a more active serum,

and finally Leclainche[794] of Toulouse, after demonstrating that the

horse is the best animal for the production of a very active serum,

succeeded in devising a method of vaccination as simple as it was

effective. He gave to it the name of “serum-vaccinations.” The first

inoculation is made with a mixture of specific serum and a culture of

living and virulent bacilli. This inoculation is well borne by all pigs

and may be made without any regard to the age of the animal. The

immunity is set up immediately after the injection of the mixture, but

it is not sufficiently durable for the requirements of practice. For

this reason Leclainche followed up the first injection by a second,

which is made ten to twelve days later and consists of an inoculation of

half a cubic centimetre of pure virus. This new method had the special

advantage of arresting, almost immediately, the mortality in an infected

piggery and of eliminating the chronic cases that are sometimes observed

after the Pasteurian vaccinations.

Leclainche[795] has already applied his method of serum-vaccinations to

more than five million pigs of all ages. “It has been found to be

constant in its effect and absolutely innocuous,” and “not a single case

of erysipelas has been met with in pigs that had received the two

vaccines,” and Leclainche hopes that his method will soon come into

general practice, and that it will be utilised in all cases where the

Pasteurian method is found to be insufficient.

[Sidenote: [499]]

As the basis of all the new methods for vaccinating pigs against

erysipelas is the preparation of serums capable of preventing the

pathogenic effect of the bacilli, the question of the determination of

the protective power of these serums comes to be one of considerable

importance. At first one was satisfied with certain approximate

estimations, but later the necessity was felt of having a more exact

measurement. Leclainche is persuaded that of all the laboratory animals

capable of being used for these experiments the pigeon is the only one

that can usefully fulfil this rôle; very susceptible to the passage

virus, it is killed by the bacillus after a regular incubation and

invasion period, and the chronic form of the erysipelas, so troublesome

in the rabbit and even in the pig, is met with in the pigeon in very

exceptional cases only. Leclainche commenced his experiments by

inoculating into the pectoral muscles of the pigeon mixtures of serum

and virulent cultures. The pigeon received 1 c.c. of a culture of a

passage virus mixed with variable quantities of serum. The serum is

ready for use in the vaccination of pigs when the pigeons resist the

injection of a mixture of ½ a c.c. of serum with 1 c.c. of a virus which

kills the control pigeons in 60 to 72 hours.

At the Frankfort Institute of Experimental Therapeutics another method

of testing devised by Marx[796] is used. In it injections, below the

skin of a series of grey mice, are made of progressively increasing

doses of the serum the strength of which it is desired to determine.

Twenty-four hours later a virulent culture of the bacillus of swine

erysipelas is introduced into the peritoneal cavity of the same mice.

The virus is so chosen that the control mice die in about 72 hours. Marx

finds that this method gives results which are much more constant and

exact than any other; this opinion is confirmed at Höchst, the largest

factory of serums in Germany.

VIII. _Vaccinations against bovine pleuropneumonia._ This infective

disease is one of the most dreaded scourges of bovine animals. Very

contagious, it has spread from central Europe not only into all the

other countries of the European continent, but into Africa, America, and

almost every quarter of the globe. The virus of this disease was

discovered in the serous exudation of hepatised lungs long before the

microbiological period of the Medical Sciences had begun.

[Sidenote: [500]]

Dr Willems of Harselt, who made an experimental investigation,

remarkable for the time at which it was carried out (more than half a

century ago), demonstrated at once the great virulence of the pulmonary

serous fluid; he found also that the effects of the inoculation of the

virus varied much according to the seat of inoculation. When made into

the trunk, the neck, or the shoulders, the inoculations are usually

fatal; at the periphery, the lower part of the limbs, at the extremity

of the ears or of the tail, the inoculation ordinarily produces merely

an inflammatory tumefaction of small extent, which is absorbed in a few

weeks; after this the animal is refractory to the natural disease.

Willems concluded from this that we may vaccinate against

pleuropneumonia by inoculating the virulent serous fluid of the lung

into the tail. Willems’ method of inoculation became a part of current

practice 50 years ago.

For the carrying out of a large number of vaccinations it is necessary

to have at one’s disposal an adequate quantity of virus; it was

therefore to meet this requirement that researches were first carried

out. The serous fluid was withdrawn from the hepatised lungs of animals

that had succumbed to the disease and was inoculated into normal Bovidae

as soon as possible, so as to avoid contamination of the fluid. In fact

this pulmonary serous fluid often contains foreign germs capable of

multiplying rapidly so that it putrefies very quickly. Pasteur showed

that it was possible to remedy these drawbacks by a very simple method

by which he could obtain a large quantity of rigorously pure virus. All

that is necessary is to inoculate a little of the pleuropneumonic virus

below the skin of a weaned calf, behind the shoulder. At the seat of

inoculation there is an abundant exudation of virulent serous fluid into

the cellular tissue, from which we are enabled to collect large

quantities of pure virus.

In some countries, as in Germany and in Australia, institutions have

been founded for the production by this method of the virulent serous

fluid necessary for these inoculations.

The virus should be inoculated into the tip of the tail of animals that

it is desired to immunise, because the temperature in this situation is

relatively low and the connective tissue is dense and not very abundant.

The inoculation is made with a lancet or a Pravaz syringe. The

vaccination is generally borne well, in spite of the reaction phenomena

which are manifested about two weeks after the introduction of the

virus. At that time a febrile condition is set up and a swelling

manifests itself at the point of inoculation, which, however, soon

retrogresses and then disappears.

[Sidenote: [501]]

The immunity conferred by Willems’ method is substantial and lasting

(for one or two years and even longer); this explains its great success

in the hands of breeders and veterinarians. Accidents following its use

are rare, and the mortality does not exceed 1 per cent.

In spite of all these advantages a new method was still desirable, a

method which would allow of the preparation of large quantities of virus

of a suitable and uniform activity under conditions of irreproachable

purity. Thanks to the discovery of the micro-organism of pleuropneumonia

which we owe to Nocard and Roux[797] this object has been achieved. With

the collaboration of Borrel, Salimbeni, and Dujardin-Beaumetz, they

succeeded in demonstrating and isolating this micro-organism, the

smallest of all known living organisms. The first steps in these

researches were very laborious, but later the organism of

pleuropneumonia was cultivated on fluid and solid media: Martin’s broth

(prepared with pigs’ stomachs) or agar with the addition of a certain

quantity (about 5%) of fresh ox serum. The serum-broth, sown with pure

pneumonic serous fluid, gives only a moderate growth, which becomes only

slightly turbid and contains micro-organisms so small that it is

impossible to distinguish them individually. They can be made out only

when massed together in irregular clumps. The minuteness of this

micro-organism is evidenced by the ease with which it passes through a

Berkefeld filter, and even through certain Chamberland candles (F). This

feature enables us to obtain the pure virus easily, a fact very

important in connection with the isolation of the micro-organism.

[Sidenote: [502]]

Once in possession of pure cultures of the micro-organism of

pleuropneumonia, Nocard and Roux attempted to make use of it in

practical vaccination. They showed that the organism separated by them

is capable of producing typical pleuropneumonia when it is inoculated

into the appropriate regions of the body of bovine animals. But when

inoculated subcutaneously or into the skin of the tail, it produces

merely a mild and transient disease which confers an immunity quite as

effectual as that set up by the inoculation of the virulent serous

fluid. It may be readily understood that, under these conditions, pure

cultures may be much more serviceably employed in the practice of

vaccination than can Willems’ virus from the fact that it is easy to

obtain large quantities of absolutely pure cultures. It is easy to

predict that the new method will soon replace the old one, very great as

are the services the latter has rendered to agriculture. Up to the

present, vaccinations with pure cultures have been made in several

districts in France with very favourable results. The Pasteur Institute

and the Veterinary School at Alfort have already distributed to

veterinary surgeons more than 5,000 vaccinal doses of culture; the

protective action of these inoculations has been at least equal to that

of the inoculations by Willems’ method and the resulting accidents have

been reduced in the proportion of 20 to 1[798].

The serum of animals hyperimmunised against pleuropneumonia possesses a

very distinct _protective_ action, but too little marked and of too

short duration to be of any use in practice; it has also a _curative_

action arresting the invading march of a pleuropneumonic congestion; but

here it is necessary to intervene early, before the appearance of fever,

and to inject large quantities of serum.

The inoculation of a mixture of virus and serum produces no congestion;

but it does not confer any immunity; the animal remains just as

susceptible as the control to the inoculation of the pure virus.

[Sidenote: [503]]

IX. _Vaccinations against typhoid fever._ In the preceding sections I

have treated more especially of the vaccination of domestic animals

against several infective diseases. The information collected on this

subject is marked by its great exactness, as it is easy to apply to

animals the most rigorous experimental method. In the case of the human

subject this is not such an easy matter. As it is impossible to submit

him to experimental proof we are obliged to be satisfied with

observation, controlled by statistical data. The experience of more than

100 years has, however, been sufficient to demonstrate the great utility

of vaccinations against small-pox with the virus of cow-pox which is

innocuous for the human subject. In the case of antirabic vaccinations

we have to deal with injections into the human subject, first of

weakened viruses and then of virulent viruses. Here, however, it is a

question of the preservation of the already infected human organism,

which, very often, only comes under treatment during the incubation

stage of rabies. One can readily understand the hesitation to inoculate

even weakened viruses into the human subject, especially when we are not

dealing with altogether exceptional cases such as we have in the

protection against rabies. We have, therefore, but few examples in which

the methods of vaccination by micro-organisms have been applied to man.

Such injections were first tried by Ferran[799] against Asiatic cholera.

Having succeeded in vaccinating guinea-pigs against experimental cholera

septicaemia, the Spanish investigator attempted to inoculate cholera

vibrios into the subcutaneous tissue of man, hoping thus to vaccinate

him against true cholera. In this way he was able to demonstrate that

the subcutaneous injection of living vibrios never sets up symptoms of

cholera. The injection is followed by a general reaction in the form of

fever, pains in the back and inflammation at the point of inoculation,

in a word, transient phenomena of little gravity. Encouraged by these

initial results Ferran, profiting by the outbreak of cholera in the

province of Valentia, injected into more than 20,000 persons living

cultures of Koch’s vibrio. The results published by him did not,

however, furnish any real proof of the possibility of conferring

immunity against intestinal cholera by means of subcutaneous injections.

Later Haffkine[800] modified Ferran’s primitive method somewhat, and

instead of living vibrios he injected vibrionic cultures killed by heat

or by antiseptics. During the cholera epidemic of 1892 and 1893 he tried

the inoculation of these killed vibrios into man, with the object of

vaccinating against Asiatic cholera. Later he went to Calcutta in order

to try his method on a large scale. He was there enabled to inoculate a

great number of persons, and the statistics which he collected appeared

to him to be favourable.

[Sidenote: [504]]

But studies on the pathogenesis of Asiatic cholera shook the foundations

of Ferran’s method. The injections of vibrios, living or killed, were

found quite capable of vaccinating animals against vibrionic peritonitis

and septicaemia, but they appear to exert no influence whatever against

poisoning by the cholera toxin. When it had been learnt how to set up

true intestinal cholera in young rabbits Ferran’s and other similar

methods of vaccination were used in vain to prevent the incidence of

this disease, which is very similar to Asiatic cholera of man. An

experiment[801] made at the Pasteur Institute in Paris upon two persons

vaccinated by Haffkine, showed that they were not protected against the

choleriform diarrhoea set up by the ingestion of the cholera vibrios. A

third person, who had never been “vaccinated” and who served as

“control,” after the ingestion of the same cholera culture, behaved

exactly as did the other two.

From all these data the conclusion was drawn that in order to prevent

intestinal cholera it is necessary to use not cultures of vibrios,

living or dead, but antitoxic serums. In fact, the majority of young

rabbits vaccinated with these serums and afterwards submitted to

infection by the cholera virus through the mouth were found to be

vaccinated against intestinal cholera. It has not been possible, as yet,

to apply this method to man, hence we are unable to give a decided

opinion. Moreover, as the methods based on Ferran’s principle have now

been abandoned I have not deemed it necessary to devote a special

section to anticholera vaccinations. I could not, however, pass it by in

silence, since the attempts to vaccinate man against cholera have led to

the trial of a similar method against typhoid fever.

Pfeiffer and Kolle[802] were the first to inoculate man with typhoid

coccobacilli sterilised by heat. They observed that these injections

caused fever, pretty violent pains in the back accompanied by vertigo,

shivering and pain at the point of inoculation, without, however, being

in any way serious to health. At the same time they found that the blood

serum of inoculated persons acquired a very marked protective power (for

guinea-pigs injected into the peritoneal cavity with lethal doses of

typhoid cultures) quite comparable to the properties discovered by them

in the serum of persons who had recovered from typhoid fever. Pfeiffer

and Kolle believed that they thus had a proof of the refractory

condition of the individuals whom they had submitted to these

injections.

[Sidenote: [505]]

These experiments were continued by Wright, Professor of Pathology at

Netley, and it is owing to his unwearied efforts that science finds

herself in possession of very important evidence on the subject of

protective inoculations against typhoid fever in man. According to a

verbal communication made to me by Wright, he has up to the present

distributed more than 300,000 doses of his antityphoid vaccine. This

vaccine he prepared in the following way[803]. The typhoid coccobacillus

is sown in carefully neutralised broth containing 1% of peptone. The

flasks of culture are kept in the incubator at about 37° C. for two or

three weeks, after which their contents are transferred to large flasks

in order to be submitted to a temperature of 60° C. This temperature is

quite sufficient to kill all the coccobacilli, but for greater surety

Wright added to his cultures one-tenth of their volume of a 5% solution

of carbolic acid or of lysol. The vaccine, thus prepared, is examined as

to its toxicity for the guinea-pig by means of subcutaneous injections.

Wright injects into man a dose of vaccine which is sufficient to kill

100 grammes of guinea-pig (of the weight of 250 to 300 grammes). This

dose often amounts to half a cubic centimetre, but it may have to be

increased to 1 c.c. and even 1·5 c.c.

The inoculations are made below the skin of the flank or in the

shoulder. They are followed by a rise of temperature which commences as

early as two or three hours after the injection. This fever is

accompanied by pains in the back, nausea, and want of appetite. There

may even be collapse; this led Wright to keep his patient in bed for

some time after the vaccinal injection. Besides this reaction, there

occurs, at the seat of inoculation, a swelling and redness, accompanied

by pain; as a rule all these symptoms have disappeared by the end of 48

hours.

[Sidenote: [506]]

Wright convinced himself that the blood serum of individuals treated by

his vaccine, at the end of a certain time acquires the property of

agglutinating typhoid coccobacilli in a variable, but usually very

marked degree. He even thought that this property might up to a certain

point serve as the measure of the immunity acquired against typhoid

fever. His own researches, however, showed him that this supposition

could not be maintained, and that the agglutinative power, varying

greatly in strength, might sometimes be absent where the immunity could

not be denied. On the other hand, he clearly showed, especially by the

experiments with serum collected at the period which precedes the

relapses, that the agglutinative property might be highly developed, in

spite of the absence of immunity. Wright then set himself to study the

bactericidal property of the serum of individuals who had been injected

with his vaccine. He devised a very ingenious method of gaining with a

minimum loss of time some idea of the fluctuations of this power of the

body fluids to kill the typhoid coccobacillus. In the first place he

demonstrated that the bactericidal property is not at all parallel to

the agglutinative power, and this has further confirmed him in his

opinion that there may be no direct relation between it and acquired

immunity. He has found further that the power of the blood serum to

destroy the typhoid coccobacillus is very variable in persons vaccinated

by his method. After injections of large quantities of these killed

bacilli this power may even be diminished for a very long period. On the

other hand, medium or small doses of the vaccine first set up a negative

stage, during which the bactericidal property is very feeble, and later

they bring about an increase of this property, often very marked. Wright

does not think that the bactericidal power can serve as the measure of

the immunity acquired by the vaccinated individuals, but he hopes that

some day a method may be found suitable for the examination of the blood

which will give us information as to the degree of immunity conferred by

the antityphoid vaccination. For the present the only basis upon which

we can form any opinion on this subject is furnished by statistics. Now

we know that it is often very difficult to collect data that are

sufficiently exact. Hence during the war in South Africa, where

one-fifth of the English troops, that is to say about 50,000 persons,

were submitted to vaccinations by Wright’s method, it is only in certain

cases that the statistical information can be utilised. Many of the

patients attacked by slight fevers are omitted from the statistics,

because from the absence of a precise diagnosis it is not known whether

they should come under the category of typhoid patients or not. In other

cases the secondary complications divert the attention of the doctors

and prevent the registration of a proper diagnosis.

[Sidenote: [507]]

Of the data collected amongst the English troops in South Africa, Wright

considers that those which were collected during the siege of Ladysmith

were the most exact, on account of the facility with which it was

possible to study and register all the cases of typhoid fever under

these conditions of complete isolation. Now it has been recognised that,

amongst the vaccinated soldiers and officers, there occurred scarcely

one-eighth as many cases of typhoid fever as occurred amongst the

unvaccinated (1,499 cases in 10,529 unvaccinated, and 35 cases in 1,705

vaccinated). The mortality amongst the vaccinated was also very much

lower. The difference to the credit of the vaccinations should in

reality be even greater, for amongst the unvaccinated are counted many

persons who having already had an attack of typhoid fever were not

submitted to vaccination.

The testimony of the majority of the medical men who followed the

results of Wright’s method closely is also favourable to the

vaccinations. Thus Henry Cayley[804] reports that the staff of a Scotch

Hospital of the Red Cross, almost all of whom (57 persons out of 61) had

received two vaccinal inoculations, escaped typhoid fever, in spite of

the numerous opportunities afforded for the contraction of the disease.

This very favourable example is also instructive in that it testifies to

the value of two consecutive vaccinations. In many other cases where one

has had to be satisfied with a single protective inoculation the results

were less brilliant. According to Howard Tooth, who made his

observations at Bloemfontein, the vaccinations according to Wright’s

method must be regarded as very useful.

Outside South Africa this method has been employed on a fairly large

number of persons in British India, in Egypt, and in Cyprus. According

to the earlier statements from India the incidence amongst the

vaccinated persons was one-third that of the unvaccinated. The most

recent statistics[805] show still more favourable results. Thus at

Meerut the incidence amongst vaccinated persons from Oct. 1899 to Oct.

1900 was one-eleventh that of the unvaccinated (2 cases of typhoid fever

in 360 vaccinated, and 11 cases of the same disease in 179

unvaccinated): the mortality (one case amongst the former, six amongst

the latter) was less than one-twelfth that of the unvaccinated.

In Egypt and in Cyprus according to the statistics communicated to Dr

Wright[806] by Col. Fawcett these vaccinations have given even better

results. In 2,669 unvaccinated persons there occurred 68 cases of

typhoid fever with 10 deaths, whilst amongst the 720 vaccinated there

was only a single case of this disease, this single case succumbing.

Here, however, we have to do with a patient who must have received the

vaccinal inoculation during the period of incubation, the disease

breaking out soon after the vaccination. This would represent in all the

cases a morbidity only one-seventeenth as intense amongst the

vaccinated.

[Sidenote: [508]]

A few isolated voices only have not pronounced in favour of the

antityphoid vaccinations and their opinion is formulated in a very

undecided fashion. Amongst the most important of these adversaries, if

indeed we may term them such, must be cited Washbourn[807], on account

of his experience in microbiology. Attached as a doctor to the Yeomanry

Hospital at Deelfontein in South Africa, he witnessed many cases of

typhoid fever and was greatly struck by the death of two persons amongst

the vaccinated patients. But he himself confesses that it is as yet

premature to judge Wright’s method, and in support of his sceptical

attitude does not offer any other satisfactory observation.

Outside the English colonies vaccinations against typhoid fever have

been tried in Russia by Wyssokowitch[808]. He inoculated 235 soldiers of

a regiment encamped at Kiew, amongst whom an epidemic of typhoid fever

had broken out. The vaccinations were carried out by means of cultures

killed with carbolic acid. We are unable to judge of the efficacy of the

method because the number of persons vaccinated was too small and the

epidemic too limited. It may be noted, however, that amongst these

individuals not one took typhoid fever, whilst amongst the unvaccinated

three cases of the disease were registered.

The antityphoid vaccinations have as yet only a very short history, and

it is, perhaps, premature to express any decided opinion on the matter.

We may, however, consider the results already obtained as offering

encouragement to continue our experiments. Everything, indeed, tends to

a recognition of the utility of vaccinations by means of killed typhoid

cultures. The statistics are as a rule good; the danger from the

protective inoculation is _nil_ or quite trifling. With the exception of

the discomfort of which we have spoken and which is transitory, no

untoward result has ever been observed.

[Sidenote: [509]]

To all this must be added the fact that from the point of view of the

pathogenesis of typhoid fever, all the probabilities point in favour of

the vaccinations. Whilst in Asiatic cholera we have to deal with an

intoxication, from the alimentary canal, an intoxication set up by

vibrionic products, against which the subcutaneous inoculation of

micro-organisms can not be effective, in typhoid fever we have to do

with a real infection. The micro-organism, although developed at first

in the small intestine, becomes generalised throughout the system.

Thanks to improved methods it can always, or almost always, be found in

the blood of the patient, and its constant localisation in the spleen

furnishes a real evidence of this. Under these conditions it is quite

natural to suppose that everything which is able to prevent the

penetration of the typhoid coccobacillus into the blood and the internal

organs ought at the same time to contribute to the protection of the

individual.

We are fully aware that science has not yet said its final word upon

this question. We are coming more and more to the conclusion that it is

necessary to make two injections instead of one. It is possible that we

may have recourse to certain improvements of the method by combining

with it the injections of antityphoid serums as a protective measure.

The near future will doubtless bring us the solution of these very

important questions.

X. _Vaccinations against human plague._ Plague, which for so long was

looked upon as the greatest scourge of humanity, has until recently

remained almost unknown from the scientific point of view. But from the

moment that it became possible to apply to its study the immense

advances realised by microbiology the thick veil which had hidden its

nature fell at a single stroke and science found itself in possession of

effective means of fighting against it. Amongst these means one of the

most important is protective vaccination.

[Sidenote: [510]]

When the last pandemic of plague broke out in Bombay and in the East

Indies in general, Haffkine was there engaged in applying his method of

vaccination against Asiatic cholera of which we have spoken in the

preceding section. Well acquainted with the results of the

bacteriological researches made on bubonic plague by Kitasato, and

especially by Yersin, he, in 1896, began to study this disease. After

the discovery made by Yersin, Borrel, and Calmette[809], who showed that

animals susceptible to human plague could be easily vaccinated against

the micro-organism which gives rise to it, Haffkine[810] endeavoured to

find a practical method for the vaccination of man. He set up a

laboratory at Bombay and, after some preliminary experiments on rabbits,

he commenced to inject human beings with pure cultures of the plague

coccobacillus. From 1897 up to the present he was able to vaccinate a

very large number of individuals, and the results obtained have

encouraged him to continue the application of his method. The principle

of this method is that which had guided him in the preparation of

anticholera vaccines and which is used for the vaccines against typhoid

fever. It consists in the employment of pure cultures of the specific

organism killed by heat. The cultures are grown in large flasks

containing peptonised broth and sown with a small quantity of the plague

coccobacilli. A little sterile butter or cocoanut oil is poured on the

surface of the fluid. Under these conditions the organism grows

abundantly and produces growths which hang down into the fluid,

reminding us of the stalactites in a grotto. This mode of development

forms one of the most typical characters of the micro-organism of human

plague. The culture flasks are kept at a temperature of about 30° C. for

five to six weeks, at the end of which period a large number of the

bodies of the micro-organisms have fallen to the bottom of the flask,

allowing much of their toxic contents to escape. The fatty layer on the

surface favours a surface development of the coccobacilli, the number of

micro-organisms in a flask being thus greatly increased.

After growing for 35 to 42 days under these conditions the cultures are

heated at 65°–70° C. for from one to three hours with the object of

killing all the micro-organisms and so rendering their injection

innocuous. To make sure of the effectiveness of this heating care is

taken to remove a small portion of the fluid and to sow it in a suitable

medium. Should this medium remain sterile the vaccine may be used. Into

adult men it is injected in a dose of 3 c.c., whilst women, children,

and adolescents receive 2–2·5 c.c., into the subcutaneous tissue.

[Sidenote: [511]]

Some hours after the injection of the vaccine the temperature rises

above normal, reaching 38°·5 to 39° C., and sometimes even 40°–40°·5 C.

This febrile condition lasts from 15 to 48 hours. It is soon accompanied

by pain, redness, and swelling at the point of inoculation. These

symptoms persist for from three to five days. The _malaise_ which

follows the vaccinations is sometimes very uncomfortable or even

painful, but never serious. Only in exceptional cases is the formation

of abscesses observed, and this is due, undoubtedly, to contamination of

the vaccines by foreign micro-organisms. The English Commission sent to

India to study plague found other micro-organisms than the plague

coccobacilli fairly frequently in the vaccine culture flasks, but, with

very rare exceptions, these micro-organisms were found to be innocuous.

By rigorously following the rules to be observed in making pure cultures

it should not be difficult to avoid this complication.

Haffkine used every effort to induce his patients to be vaccinated a

second time, being justly persuaded that two injections are capable of

ensuring a more certain and more stable immunity than is a single

injection.

[Sidenote: [512]]

From what moment immunity may be considered to be acquired has been a

matter for great discussion. From very numerous experiments upon animals

of various species, as well as many observations on man, it is now

agreed that a period of several days (5–8) from the injection of the

vaccine is required before immunity is manifested. It is for this reason

that cases of plague which have broken out before this period has

elapsed cannot be looked upon as contraindicating the efficacy of the

method.

A large amount of evidence, coming from persons who have made their

observations on the spot, is almost unanimous in endorsing the fact that

Haffkine’s vaccination protects man against plague. It is often

difficult to compile exact statistics in surroundings where so many

factors contribute to deceive even the careful observer. In spite of

this a certain amount of evidence has been collected which may be

accepted as affording us fairly satisfactory information. One of the

best groups of statistics was that collected at Damaun, a Portuguese

possession in India, into which plague was imported from Bombay in 1897,

and where a large number of vaccinations were carried out. From the

report of Haffkine and Lyons[811], in a population of 8230 persons,

rather more than one-fourth (2197) were vaccinated, the greater majority

(6033) remaining uninoculated. Amongst the former only 36 died from

plague, which corresponds to 1·6 per cent.; whilst amongst the

unvaccinated persons the disease carried off 1482 persons or 24·6 per

cent. Vaccination, therefore, according to these statistics, must have

brought down the mortality to one-fifteenth. The German Commission[812],

two members of which, Koch and Gaffky, went to Damaun to be present at

the vaccinations and to observe their efficacy, pronounced in favour of

Haffkine’s method. The English Commission[813] made reservations and

criticised the statistics of Haffkine and Lyons (who amongst others

attribute all the cases of deaths that occurred amongst the unvaccinated

to plague), but in the end this Commission also recognised the utility

of the vaccinations at Damaun.

The data collected with regard to the vaccinations at Undhera, Hubli,

and several other places in British India confirm the results obtained

at Damaun. The statistics collected at these localities are certainly

open to criticism, but the result as a whole is none the less

encouraging as regards this method of vaccination. According to the

conclusions of the English Commission the “inoculations had a

considerable effect in warding off plague attacks from the

inoculated.... The protection afforded by inoculation seems, however,

never to be absolute[814].” We do not, as yet, know the duration of the

immunity produced by Haffkine’s vaccinations; it cannot be very long to

judge from the experiments on animals, but it may last for several

weeks, probably even for months.

The vaccinations by killed cultures may be especially useful when it is

a question of limiting the extension of an epidemic that is already

established. The ease with which the vaccine can be prepared renders it

possible to obtain very large quantities of it in a short time, with

which it is possible to immunise the entire population of towns or

districts. But, as the immunity by this method requires several days for

its development and as the injections of micro-organisms, even when

killed, may be very injurious during the incubation period of plague or

immediately before the infection, it is necessary to limit the

vaccinations to persons who are not in intimate contact with the sick,

or who are, from the beginning, exposed to infection[815].

[Sidenote: [513]]

Lustig and Galeotti[816] have described another method of preparing

antiplague vaccine which can be utilised where it is of importance to

obtain a large quantity of vaccine in a very short time. Instead of

allowing the cultures to grow for five or six weeks as required by

Haffkine’s method, the Italian observers make use of cultures on agar

which have grown for two days only. The micro-organisms, removed from

the surface of the agar, are treated with a weak solution of potash

(0·75%–1%) which dissolves the bodies of the coccobacilli. This

phenomenon has sometimes occurred by the end of twenty minutes, but it

often requires an hour or more. The contact of the micro-organisms with

the alkali must never exceed three hours. The viscous mass thus obtained

is then treated with acetic acid, when a precipitate is thrown down.

This precipitate, after being washed, is used for the vaccinations. When

injected in large quantities into animals, Lustig and Galeotti’s product

sets up necrosis, but a weak dose is well borne and confers immunity

against plague. In man it is sufficient to inject two or three

milligrammes of this substance diluted with water. The vaccinal nuclein

of the Italian observers has been but little employed for the

immunisation of man in India, but it is largely used in this country for

the inoculation of horses from which to obtain an antiplague serum.

[Sidenote: [514]]

The serotherapeutics against human plague were inaugurated by the

researches of Yersin, Borrel, and Calmette (_l.c._), who demonstrated

that animals susceptible to the plague bacillus can be vaccinated and

even cured of experimental plague. The preparation of antiplague serum

has since been energetically pursued under Roux’s direction at the

Pasteur Institute. After several trials, some of which were very

encouraging, others, on the contrary, somewhat unfavourable, they

succeeded in obtaining a serum which is capable of curing plague after

it has broken out and has become grave. As in this treatise we

intentionally leave aside everything connected with healing we shall

speak only of the antiplague serum as a protective agent.

Whilst vaccinations by killed plague cultures have been practised

principally in the East Indies, the immunisation with antiplague serum

has been employed in Europe, especially at the time of the epidemics of

Oporto in 1899 and of Glasgow in 1900. In all these cases use was made

of the serum from the Pasteur Institute, up to the present the most

active of all those prepared. It is a serum obtained from horses treated

for a long period with cultures of the plague bacillus and with the

toxin of the same organism. Treatment is begun by injecting plague

coccobacilli killed by heat (70° C.). These injections are made into the

veins, with the object of avoiding the local lesions which are observed

after the subcutaneous introduction of micro-organisms. When the horses

have been rendered refractory by this treatment with dead

micro-organisms, the next step is to inject (also into the veins) small

quantities of living cultures. The doses of these cultures are gradually

increased, and end by conferring upon the animal a very strong immunity,

which is strengthened by injections of products of cultures passed

through a Chamberland filter.

Calmette and Salimbeni[817] injected prophylactically more than 600

persons menaced by plague at Oporto. These comprised the doctors and the

staffs of the laboratories of hygiene and of the disinfection services,

the firemen who removed the sick persons and the dead, the families of

those who were attacked, the members of the French colony, etc. Into

each person 5 c.c. of serum was injected below the skin of the abdomen.

These vaccinations in some cases caused nettle-rash, eruptions similar

to those so often observed after the injection of the other kinds of

serums. Of the total number injected two persons contracted plague: the

unfortunate Doctor Camera Pestana and his assistant. The former

succumbed to the disease, but the second only contracted a very mild

form of it. The study of these 600 cases, as well as of experiments on

animals, demonstrated that the immunity conferred by the antiplague

serum is set up immediately after its injection but is not of long

duration. It is probable that it lasts for 8 or 10 days, or at furthest

a fortnight only.

Similar results were obtained at Glasgow. Van Ermengem[818], who has

published a report on the epidemic in this town, mentions that more than

70 persons in good health were inoculated with the serum; each one

received 10 c.c. beneath the skin of the belly. Of these 70 persons one

was attacked with a fairly mild plague 8 days after the vaccination, and

another, a housekeeper, was attacked, 9 days after the injection, with a

congestion of the cervical glands induced by the plague bacillus. Both

cases recovered. All the other vaccinated persons, in spite of constant

exposure to the plague infection, remained unaffected. Van Ermengem was

of opinion that the two persons treated with the serum were already

infected when they were vaccinated.

[Sidenote: [515]]

The Belgian observer points out, further, the frequency of secondary

accidents which were produced in the persons vaccinated at Glasgow. Van

Ermengem himself went through the ordeal after being injected with 10

c.c. of serum as a protective measure and this gave occasion to several

critics to attack the Pasteur Institute. This is how Van Ermengem

himself puts the matter. “The accidents after the immunising

injections ... were very numerous, they were observed 33 times in 72

cases. Sometimes they were even fairly serious, to the point of causing

great suffering to the patient and of disquieting those around them. We

could describe them from thorough knowledge, since we experienced them,

but they scarcely differ from those which are observed from time to time

after the injection of antidiphtheria serum, and, like them, they

disappear without leaving the least trace” (_l.c._ p. 18).

In spite of these accidents and the necessity of renewing frequently

(every ten or fifteen days) the protective injections of serum, their

use is quite advisable in certain circumstances. They may render great

service on board infected vessels or in lazarettos (as in the case which

occurred at Frioul after the arrival at Marseilles of Arab stokers

suffering from plague), in docks, warehouses, and stores where

contaminated merchandise is found. They should also be employed to

vaccinate those coming into immediate contact with plague cases in

hospitals and in private houses. In a word, vaccinations by serum, owing

to their power of conferring a very rapid immunity, should be practised

wherever there is more or less immediate and imminent danger. Under

these conditions they are of very great service in localising the

disease.

The methods of vaccination against plague that have been employed up to

the present may undoubtedly be improved. Calmette and Salimbeni (_l.c._)

have already published the results of experiments on animals undertaken

with the object of studying the effect of a combined method of

vaccination with antiplague serum and killed cultures of the plague

bacillus. But even in their present form the methods used for protecting

individuals against this disease deserve to be regarded as conferring

great benefits on humanity.

[Sidenote: [516]]

XI. _Vaccinations against tetanus._ Tetanus unlike plague is not a

contagious disease, nor is it capable of becoming epidemic. It

constitutes, however, a very formidable disease against which all

therapeutic methods have only a very limited effect. This is a further

reason for drawing the whole attention of medical and veterinary men to

the prevention of tetanus by vaccinal injections. Tetanus is a disease

in which the intoxication plays an altogether dominant part. The tetanus

bacilli do not develop, at the point where they are introduced into the

body, unless favoured by auxiliary conditions, such as the

multiplication of other micro-organisms. Even then the organism of

tetanus reproduces itself with difficulty, and without becoming

generalised throughout the body. The poison which it secretes is however

sufficient to produce a very grave intoxication, ending most frequently

in death. In certain countries tetanus, as a sequel to various wounds,

is very frequently met with in man and in certain domestic animals, such

as the horse, donkey, pig, etc.

It is only since the discovery by von Behring and Kitasato of an

effective method of immunisation against tetanus that it has been

possible to consider the practical application of antitetanus

vaccinations. These observers demonstrated that the tetanus poison, when

treated with trichloride of iodine, had its toxic action weakened and

was transformed into an effective vaccine. Roux and Vaillard found that

the addition of Lugol’s iodo-iodurated solution to the tetanus poison

renders it capable of vaccinating all kinds of susceptible animals. It

was shown later, that even with modified active tetanus toxin, we can

still obtain good results when care is taken to inject the poison with

great circumspection.

But it is not these vaccines obtained from tetanus cultures that have

come to be used in practice. The best results are obtained by the use of

antitetanus serums. After von Behring and Kitasato’s discovery of the

power of the serum of animals immunised against tetanus to neutralise

the action of the tetanus poison, very numerous experiments were made on

the same subject. It has now become possible by treating horses with

large quantities of tetanus toxin to obtain specific serums of

extraordinary activity. Thus several serums are capable of preserving

mice against a lethal dose of tetanus poison if we inject into them a

quantity of serum equal to the one-thousand-millionth of their weight.

Serums of this strength protect domestic animals against tetanus. We

know that many operations on horses, sheep, goats, pigs, and other

mammals are very often followed by a tetanus which is usually fatal.

Castration, amputation of the tail, the ablation of proud flesh or

tumours, the operation for cryptorchitis or hernias, etc. are often

complicated by tetanus. Moreover, tetanus may frequently appear in

horses that have received wounds in the foot or in the lower parts of

the limbs, “Clous de rue,” farrier’s punctures, wire-heels, blows, etc.

[Sidenote: [517]]

With the object of remedying this state of things Nocard[819]

distributed to veterinarians about 70 litres of antitetanus serum to be

employed for protective purposes. The majority of the animals treated

(horses, donkeys, mules, bulls, rams, lambs, and pigs) received two

injections of serum at an interval of 10–12 days, 20 c.c. for large

animals and 6–10 c.c. for sheep and pigs. Of 3088 animals which received

the first injection of serum immediately after the operation not a

single one contracted tetanus. Of 400 animals which received the first

injection at a later period, 1–4 days and more after the accidental

wound of which they had been the victims, one horse only, treated five

days after the accident (farrier’s puncture), was seized with mild

tetanus, but it soon recovered. In the same localities where the results

of the vaccination were so brilliant, 314 cases of grave and fatal

tetanus occurred amongst animals operated upon or injured that were not

submitted to the serum treatment.

It may be readily understood with these facts before us why the practice

of protective vaccinations of animals against tetanus should have spread

so rapidly amongst veterinarians. The demand for antitetanus serum from

the Pasteur Institute of Paris for veterinary use increases every year

at a great ratio. Thus in 1896 there were sent out only 1511 bottles of

10 c.c. each, in 1898 the number rose to 24,959 bottles, in 1900 it

exceeded 43,000.

The efficacy of the antitetanus serum employed as a protective agent can

no longer be questioned, but it must not be forgotten that its injection

does not render the treatment of the wounds unnecessary. These wounds

should receive a rigorous antiseptic cleansing. All foreign bodies

should be carefully extracted; otherwise the prolonged presence of

tetanus spores might set up a late tetanus after the disappearance of

the transient immunity due to the serum.

[Sidenote: [518]]

The protective injections of antitetanus serum into men likely to

contract tetanus are also beginning to spread. It often happens that

bicyclists, in falling, receive injuries which are contaminated by

horse-dung or other matters which may contain the spores of tetanus. In

these cases, as in many other forms of injury, vaccination with

antitetanus serum is indicated. Thus it happens from time to time at the

Pasteur Institute that injured persons come and ask for a protective

injection of serum. Several medical men and surgeons are now accustomed

to vaccinate such of their patients as have had their wounds

contaminated by earth or dung. All the cases of this treatment which

have come to our knowledge have been followed by very good results.

XII. _Vaccinations against diphtheria._ Antidiphtheria vaccinations have

been the subject of much discussion since the discovery of the

antidiphtheria serum and its introduction into routine practice. A large

number of works were published for and against the application of serum

in protective treatment against diphtheria, especially in the early

years of its use. Later the controversy has subsided somewhat, and at

present very few writers are found who continue to decry antidiphtheria

vaccinations.

The antidiphtheria serum was discovered in 1890 by von Behring working

in collaboration with Kitasato; these observers demonstrated in

laboratory animals its neutralising action upon the diphtheria toxin. A

little later von Behring began to apply it in the treatment of

diphtheria, but the early results were far from satisfactory, and von

Behring soon recognised that it was necessary to obtain much more active

serum. Along with Ehrlich of the Institute for Infective Diseases at

Berlin he set to work to study this problem. In collaboration with

several investigators, among whom I may cite Wernicke, Wassermann, and

Kossel, he succeeded in obtaining very encouraging results as regards

the antitoxic strength of the serums and their therapeutic action on

children attacked by diphtheria.

At this time, also, Roux in Paris began, assisted by Martin and

Chaillou, to study the same question. These observers prepared serums

which for that period were very active and made a very effective

application of them upon more than 300 diphtheria patients.

From the year 1894 the use of serum began to spread in all countries,

and it was then that an attempt was made to apply it to the protection

of children in good health, but who had been specially exposed to

contagion.

[Sidenote: [519]]

It was necessary to have at command large supplies of antidiphtheria

serum; this was prepared by injecting into horses repeated doses of the

toxin manufactured by the diphtheria bacillus. The serums thus obtained

were first tested as to their protective, antitoxic, and curative action

on guinea-pigs, animals very susceptible to diphtheria. The necessity of

finding some means of measuring the strength of the serum soon arose.

Von Behring and Wernicke at first standardised it on the basis of the

number of grammes of guinea-pig which could be protected by one gramme

of serum. Later, von Behring[820] introduced the principle of the

“normal serum,” that is to say, a serum of which 0·1 c.c., mixed with 10

lethal doses of diphtheria toxin, is capable of preventing every morbid

symptom in a guinea-pig weighing 300 to 400 grammes.

Ehrlich[821] perfected this method in the following way: to tubes, each

containing 10 lethal doses of a standard toxin, are added different

amounts of serum. These mixtures are brought to the same volume of 4

c.c. by the addition of physiological saline solution, and each is

immediately injected below the skin of a guinea-pig. If 0·1 c.c. of a

serum completely neutralises the 10 lethal doses of toxin, the serum

retains its name of normal serum; in the case where 0·05 c.c. is

sufficient to bring about the same result the serum is designated double

normal serum. When 0·001 c.c. gives the same results, a hundred times

normal serum, and so on. A cubic centimetre of normal serum (that is to

say a dose capable of neutralising 100 lethal doses of standard toxin)

constitutes an “immunising unit” (Immunisirungseinheit (I.E.) of

Ehrlich). As it was soon recognised that toxins, even when kept under

the best conditions, lose more or less of their toxic power, Ehrlich had

to modify his method of standardising serum. He now makes use of a

standard antidiphtheria serum, kept in a dry condition, which is much

more constant than are the toxins. Solutions of this standard serum are

prepared and compared with the serum whose strength has to be

determined. Ehrlich has given a detailed description of the method of

procedure required to obtain exact results.

[Sidenote: [520]]

At the Pasteur Institute Ehrlich’s method has been adopted, supplemented

however by another test for the estimation of the strength of

antidiphtheria serums, a method allied to von Behring’s old method.

Various doses of the serum to be examined are injected subcutaneously

into guinea-pigs, and 24 hours later these guinea-pigs receive a

quantity of a living culture of diphtheria bacilli which kills control

animals in 30 hours. The protective power of the serum in relation to

the weight of the animal is thus determined. For example, a serum which

is said to be active at 1/100,000 has the power, in a quantity equal to

1/100,000th of the weight of the inoculated guinea-pig, of preventing a

fatal result. It was thought, at first, that the protective power,

measured in this way, would be proportional to the antitoxic property

determined according to Ehrlich’s method. But as the results given by

these two methods were often widely different, it was resolved at the

Pasteur Institute to examine by both methods all the serums intended for

use in practice. This led to the conclusion formulated by Roux[822], in

his report communicated to the International Congress of Hygiene, held

at Paris in 1900, that a serum possessing a very high protective power

(against the living diphtheria bacillus) might be only feebly antitoxic,

and _vice versâ_.

[Sidenote: [521]]

This result is explained by the fact that the antidiphtheria serums are

very complex fluids, containing several superposed properties of very

variable strength. Marx[823], of the Frankfort-on-Main Institute, tried

to shake Roux’s conclusions, bringing forward his experiments made on

guinea-pigs and rabbits injected with antidiphtheria serum into the

peritoneal cavity and into the veins. He wished in this way to avoid the

introduction of the serum into the subcutaneous tissues, whence the

absorption of the antitoxin must take place in a very irregular fashion.

In Marx’s experiments, thus carried out, the protective power of the

serums was always found to run parallel with their antitoxic power, from

which he concluded that Roux’s view was incorrect. It must not be

forgotten, however, that this view was founded on experiments in which

the antitoxin had been injected into the subcutaneous tissue before or

simultaneously with the toxin or the diphtheria bacillus. Under these

conditions the protective power is often found to be altogether

disproportionate to the antitoxic power. This fact has been observed so

carefully and with such exactness that it is impossible to deny it. Now

it is undoubted that the conditions of the experiments upon which Roux

relies correspond much more closely with those that are realised in

vaccination of man against diphtheria than with the conditions met with

in Marx’s experiments. In these vaccinations antidiphtheria serum is

injected below the skin of persons whom it is wished to protect against

the action of the diphtheria bacillus.

With the object of bringing about a unification of the methods of

estimating serums used in different countries the International Congress

of Hygiene, held at Madrid in 1898, appointed a special Commission to

settle this problem. But when the Congress met again at Paris in 1900

this Commission had not completed the task allotted to it. The

representatives of the various methods had exchanged ideas, but in

applying the same method the results obtained in various places and by

various observers presented differences too great to allow of any

understanding being arrived at. It is evident that we have here a very

complicated problem. The serums are tested on living animals in which of

course nothing like the constancy of a chemical reaction can be

obtained.

Possibly the methods of breeding and the races of the same animals in

the different countries may be quite sufficient to explain the

divergencies in the results obtained. Whatever may be the reason the

unification of serum estimation has not yet been obtained, and it is

difficult to anticipate that any better result is to be arrived at.

From all this we may draw the conclusion that the possibility of

attaining a too rigorous precision in the standardisation of serum has

been exaggerated. Our object must be to obtain results as favourable as

possible in the application of the antidiphtheria serums, and for that

purpose it is necessary to inject greater quantities than those which

may be indicated by any method of estimation. This rule is applied as

far as is possible at the Pasteur Institute.

As regards vaccination against diphtheria of persons who are in good

health but are especially exposed to infection, the question must be

accepted as settled in the affirmative.

[Sidenote: [522]]

From the commencement of our attempt to cure diphtheria by means of a

specific serum, the necessity was seen of protecting children who were

in contact with the sick persons against this disease. Small quantities

of serum were injected into such children for protective purposes. The

first results communicated in 1894 by Roux to the Congress at Budapest

being very encouraging, an attempt was made to give the greatest

possible extension to the system of vaccination by antidiphtheria serum.

In the following year, 1895, fairly numerous statistics had been

collected, and Torday[824] at Budapest, Kurth[825] at Bremen, and

Rubens[826] at Gelsenkirchen were able to publish a number of favourable

statistics. Soon afterwards, however, a fatal case occurred in the

family of a well-known Berlin doctor, Langerhans[827], an accident that

started a violent controversy and stirred up an active campaign against

serum. Langerhans’s son, a boy aged 2 years, in good health, was

inoculated with a small dose (1·2 c.c. of this serum) and succumbed

about a quarter of an hour afterwards with symptoms of suffocation. The

post-mortem examination made by Strassman[828] showed the cause of death

to be suffocation in consequence of the aspiration of food into the

respiratory passages during the act of vomiting. An examination of the

serum used by Langerhans did not reveal any toxic action on animals or

any contamination by micro-organisms. All to no purpose, the serum was

held answerable for the death of the child, and an attempt was made to

demonstrate at almost any cost that its use in human practice was

extremely dangerous. Gottstein[829] joined in chorus with the

over-excited opinion and published a denunciation of vaccinations by

antidiphtheria serum. He collected from the literature of both

hemispheres four cases, in all, in which death had occurred some time

after the injection of this serum into children not suffering from

diphtheria. A perusal of the description of these cases is sufficient to

convince one that the death could in no sense be attributed to the

serum, and that it could be explained much more easily by the fatal

action of the streptococcus, the cause of the non-diphtheritic

affections of the children that died.

[Sidenote: [523]]

The ineptitude of this denunciation must have done much to calm public

opinion, and in September of the same year, 1896, C. Fränkel[830], in a

report presented to the German Association of Public Hygiene, was able

to give a review of the state of the question of vaccination against

diphtheria, summing up in favour of the use of the specific serum.

“Taking into consideration the data collected,” he remarks, “it is

scarcely possible to doubt the value of immunisation by serum, so that

we may say positively that we are now treading a path which will lead us

to great and important results.” This very favourable opinion was due in

great measure to the vaccinations carried out in the wards of Heubner’s

Clinic at Berlin[831]. At first, injection of the antidiphtheria serum

as a protective into patients who were found in the immediate vicinity

of the children attacked with diphtheria (contacts) was deemed to be

sufficient: but in consequence of the results obtained by this method it

was decided (starting from January, 1896) to inject all children who

came into the hospital. During the first period there still occurred a

few cases of diphtheria contracted in hospital, but from the moment

systematic and general vaccinations were introduced not a single new

case occurred.

The immune condition of the vaccinated children is maintained for three

to four weeks. After this lapse of time some of them contracted

diphtheria. But it was sufficient to introduce revaccination at the end

of this period to prevent the outbreak of any further case of diphtheria

in Heubner’s wards. Results quite as favourable and as convincing were

obtained in the department for children attacked by scarlet fever.

[Sidenote: [524]]

The amount of serum injected varied, but it was usually given in doses

of 1 c.c. containing from 200 to 250 I.E. (immunising units of Ehrlich).

The serum was always found to be innocuous except in certain cases where

it set up erythemata of greater or less extension. In 460 injections 20

cases of these exanthemata were produced, that is to say 4·34%. The

frequency of these complications was not proportional to the amount of

serum injected. According to the figures communicated by Löhr the

largest doses of the serum employed did not produce exanthemata more

frequently than did the smaller quantities. Thus 117 injections of 1

c.c. only were followed in five cases by these erythemata, which

corresponds to 4·27 per cent. The hope of diminishing the frequency of

the exanthemata by diminishing the amount of serum injected was

therefore not realised. This fact lends support to the conclusion above

formulated as to the exaggeration of the importance of the measurement

of serum. If it could be established that small quantities of serum rich

in antitoxin caused cutaneous eruptions less frequently than did

stronger doses there would certainly be a great advantage in using

serums containing a very large number of immunising units for

vaccination. Perhaps serums having a great antimicrobial power but of

comparatively low antitoxic potency might even render great service in

protective treatment. Future researches undertaken in this direction

alone can give us information on this subject.

In 1896 the vaccinations in Heubner’s wards were discontinued, but the

reappearance of diphtheria in 1897[832] rendered their recommencement

necessary. 500 children were vaccinated each with 200 immunising units.

Following this no case of diphtheria broke out. The eruptions were rare

and slight.

The increasing extension of the use of antidiphtheria serum for the cure

of the disease after it has broken out has led to a greater development

in its use as a preventive measure. Thus, in the countries where

diphtheria is endemic, vaccinations by serum are now practised very

extensively. In Russia, which is one of the great hotbeds of this

disease, vaccinations by antidiphtheria serum are frequently practised.

[Sidenote: [525]]

At the Congress of Russian doctors at Kasan in 1896, Vissotsky

communicated the result of 2,185 vaccinations which gave a morbidity of

1·3%, a morbidity that must be regarded as very low indeed. A well-known

Russian physician for children’s diseases, Rauchfuss[833], who cites

these figures, has collected several other facts concerning the

prophylactic injections of antidiphtheria serum followed by good

results. In the government of Woronetz, according to the statements of

Ouspensky[834], out of 738 vaccinated persons diphtheria occurred in 2·2

per cent., which again may be considered a favourable result, especially

if we take into account the great extension of diphtheria in this

country. In Podolia, out of 537 children vaccinated in 1895, only four

cases of diphtheria occurred, a morbidity of 0·74%. In the government of

Kherson, one of the great centres of diphtheria in southern Russia, the

results appear to be less favourable: out of 543 children which received

a protective inoculation, 21 contracted the disease (or 4·6 per cent.),

of which five died. If we study these statistics more closely[835] it

will be seen that these results are far from being unfavourable. The

protective inoculations were made only once and with somewhat small

doses, nevertheless many of the cases of diphtheria broke out only at a

late period, sometimes more than nine months after the injections had

been made. Now, it is proved that these injections, although very

efficacious, produce their action for a very short time only, for a few

weeks at most. Of the five fatal cases, four did not occur until 2, 4½,

6, and 9½ months respectively after the protective inoculation. It is

impossible to look upon these statistics as affording proof of the

inefficacy of the serum. The fifth case is the only one that occurred

within a short time (15 days) of the injection, and in this instance

only 150 immunising units had been injected.

A detailed study of the other examples of antidiphtheria inoculations in

the government of Kherson leaves a very favourable impression. Out of 90

children inoculated by Wecker[836] in the district of Elisabetgrad not a

single one contracted diphtheria, which is the more remarkable as at the

time of the inoculations there existed in the same families 14 cases of

diphtheria; the chances of contamination were thus great.

[Sidenote: [526]]

Recently, on the occasion of the outbreak of a great epidemic in Paris,

the question of vaccinations by serum was again raised and earnestly

discussed at the Paris Hospitals Medical Society and at the Society for

the Study of Children’s Diseases. Voisin and Guinon[837] communicated

the history of an epidemic amongst the staff at the Salpêtrière Hospital

in the wards of idiot children, “against which protective serum

treatment was remarkably effective and absolutely innocuous.” The serum

was injected, in the case of children more than 10 years of age, in 10

c.c. doses, and into the rest in 6 c.c. doses. This measure brought

about first an abatement and then cessation of the epidemic. The

immunity after a single injection lasted from two to three weeks, and

the few cases of diphtheria which broke out amongst the infected

children were distinguished by their great mildness. Erythemata and

other post-injection complications were insignificant, so that the

protective use of the serum was fully justified. Only a small minority

of the medical men who took part in the discussion spoke against the

antidiphtheria vaccinations; once, indeed, a reference was made to the

case of Langerhans’s child, although its death was certainly not due to

the serum. It is true that in families where it is possible to keep the

children under careful observation and to intervene at the appearance of

the first symptoms of diphtheria, the preventive injections may be

dispensed with, but in practice these favourable conditions are rarely

realised, and the prophylactic serum treatment is then of great service

in preventing the outbreak of the disease.

Netter[838] communicated to the Society of Pediatrics a summary of

32,484 observations on the prophylactic injection of antidiphtheria

serum. Of this number 192 cases were noted in which the diphtheria broke

out in spite of the injections, corresponding to 0·6 per cent. of those

treated. These figures, however, included all cases of the disease which

occurred up to thirty days after the injection. Now, the immunity is

often less durable than this, and it may disappear more or less

completely twenty days and sometimes even fifteen days after

vaccination.

Netter himself made great use of antidiphtheria vaccination. It was his

custom to propose to the parents either a protective inoculation at once

or a systematic precautionary bacteriological examination of the throats

of the children not yet attacked. He regards the first method as

preferable. According to the latest statistics which he was kind enough

to communicate to me, of 152 children (in 50 families), 91 of whom

received protective inoculations, not one contracted diphtheria: whilst

in 239 other families where the children had not been inoculated there

were 52 cases of diphtheria, with 10 deaths. Many practitioners in Paris

have now pronounced themselves in favour of protective injections of the

serum, and the Society of Pediatrics, at its meeting on 11th June, 1901,

concluded the discussion of this question by proposing the following

resolution: “The Society of Pediatrics, affirming that protective

inoculations present no serious danger and confer a very considerable

amount of immunity for some weeks, recommend their use when children are

gathered together in numbers, and in families where a scientific

supervision cannot be maintained.”

The large amount of evidence collected on this question leaves no doubt

as to the real efficacy of vaccinations by antidiphtheria serum.

[Sidenote: [527]]

The summary of the results obtained by vaccination in the 12 diseases of

man and of animals I have just placed before my readers cannot pretend

to serve as a detailed guide to prophylactic practice. My object has

been merely to concentrate into one chapter the principal data upon

which this very important question rests, to bear witness to the

progress which has already been realised, and at the same time to show

that the scientific study of immunity is in very intimate relation with

its practical application. It is evident that the road is far from

traversed to its terminus, for there are many infective diseases in

which vaccinations cannot be employed, but it is none the less certain

that the path which has led to so many important and useful results

should still be followed in studying problems which up to the present we

have been unable to solve.

CHAPTER XVI

HISTORICAL SKETCH OF OUR KNOWLEDGE ON IMMUNITY

Methods used by savage races for vaccination against snake venom and

against bovine pleuropneumonia.—Variolisation and vaccination

against small-pox.—Discovery of the attenuation of viruses and of

vaccinations with attenuated micro-organisms.—Theory of the

exhaustion of the medium as a cause of acquired immunity.—Theory

of substances which prevent the multiplication of micro-organisms

in the refractory body.—Local theory of immunity.—Theory of the

adaptation of the cells of the immunised organism.

Observations on the presence of micro-organisms in the white

corpuscles.—History of phagocytosis and of the theory of

phagocytes.—Numerous attacks upon this theory.—Theory of the

bactericidal property of the body fluids.—Theory of the antitoxic

power of the body fluids.—Extracellular destruction of

micro-organisms.—Analogy between bacteriolysis and

haemolysis.—Theory of side-chains.

Progress of the theory of phagocytes.—Attempts to reconcile it with

the humoral theory.—Present phase of the question of immunity.

[Sidenote: [528]]

As protection against disease is one of the most important amongst those

questions which are engrossing the attention of humanity, it is natural

that very great attention should have been devoted to it from the most

remote times. We see primitive races, the ordinary layman, medical men,

legislators and even the most subtle thinkers devoting their energies to

the solution of the problem of immunity against poisoning and against

infections. Historical science will never reveal to us the earliest

sources of our knowledge on this question, so remote are their origins.

The wide distribution of several methods for protecting man and cattle

against certain diseases clearly proves that the origin of this practice

dates from a very early period.

[Sidenote: [529]]

The frequency of venomous snakes in many countries has inspired a dread

of these reptiles, and this must have led to the search for some method

of fighting against the poisoning after the patient had been bitten.

Thus, we find that many primitive races make use of various methods of

immunising the body against the action of venom. The Portuguese colonel,

Serpa Pinto[839], in a letter addressed to d’Abbadie, describes the

method by which he was vaccinated by the Vatuas, natives of the east

coast of Africa. These savages extract the poison of snakes and prepare

from it, by the addition of vegetable substances, a very brown glutinous

paste which they introduce into incisions made in the skin. This

operation is very painful and is followed by a swelling which lasts for

a whole week. The Vatuas assert that this method confers a sure immunity

against the venom. Serpa Pinto was never bitten by a snake, but, a short

time after he had been vaccinated, he was stung, in the Seychelles

Islands, by a scorpion without experiencing any ill effects. This

experience confirms the assertion of the Vatuas, because it has been

shown that the vaccine against snake venom is also efficacious against

the bite of scorpions. The fact that after being stung by another

scorpion ten years later Serpa Pinto was so ill that for eight days he

believed that he was going to die or at least to lose an arm, shows that

he did not enjoy natural immunity, and the innocuousness of the previous

bite must therefore be attributed to a vaccination the effect of which

had disappeared at the end of ten years.

Another vaccinal method used by primitive races is that against the

pleuropneumonia of the Bovidae. De Rochebrune[840] points out that the

Moors and the Pouls of Senegambia have “a custom whose origin is lost in

the obscurity of antiquity” which consists in the inoculation into their

herds of cattle of the virus of the epizootic pleuropneumonia. “The

point of a knife of primitive form, or of a dagger, is plunged into the

lung of an animal that has died from the disease and an incision,

sufficient to allow the virus to penetrate below the skin of the healthy

animal, is made into the supranasal region. Experience has demonstrated

the success of this protective operation.”

In Europe, the vaccinations of cattle with the virus of pleuropneumonia

have certainly been known for more than a century, for, in a pamphlet

published at Berne in 1773[841], mention is made of the “inoculation” of

Bovidae as a means of preventing the disease in England and in Holland,

a disease against which it has been recognised that remedies are

powerless.

[Sidenote: [530]]

The inoculation of the variolous virus into the healthy human subject,

which comes into the same category as the inoculation of the

pleuropneumonic virus into healthy bovine animals, is also a widely

extended and very ancient method. The Chinese[842] assert that they have

known from the commencement of the 11th century the method of immunising

against small-pox. Amongst them, as amongst the Siamese, the matter from

the variolous scab is introduced into the nostrils. In Persia

variolisation is practised by surgeons and by the staffs of bathing

establishments, who introduce the powdered scabs into scratches in the

skin. The Ashantis inoculate the variolous virus into seven places on

the arms and legs. According to the account of Timoni, a Greek physician

practising in Constantinople in the first half of the 18th century, the

Circassians and Georgians, intent upon preserving the beauty of their

daughters, make punctures at various points in the skin, with needles

charged with variolous virus. Everybody is acquainted with the fact that

it was from Constantinople that Lady Mary Wortley Montague at the same

period (1721), imported into Europe “the Greek method,” which consisted

in the inoculation of the contents of small-pox pustules with the object

of producing a benign small-pox and of protecting the vaccinated person

from severe and dangerous small-pox. This practice was widespread in

Europe during the second half of the 18th century, but as it was not

unattended by serious drawbacks an attempt was made to avoid them by the

employment of all kinds of medicaments. As these, however, were found to

be entirely ineffective, the need was felt of replacing variolisation by

some more benign method.

[Sidenote: [531]]

It is asserted[843] that in Baluchistan the custom of having cows

suffering from cow-pox milked by children who had wounds on their hands

has been widespread from time immemorial. This practice conferred upon

these children an immunity against small-pox. It cannot be denied that

the idea of being able to vaccinate with cow-pox was common knowledge

amongst breeders and dairymen in several countries in Europe, especially

in England, France, and Germany. It is stated that Edward Jenner learnt

from the country people of his native county of Gloucestershire that

contact with cow-pox protected against small-pox. Being a man of great

understanding and culture, he set himself to verify this opinion

experimentally. Having demonstrated by a great number of experiments

that the inoculation of variolous virus into persons vaccinated by

cow-pox had no ill result, he became the great propagandist of the new

method. He worked at this subject for 20 years but only decided to

publish his results (in 1798) after he had completely satisfied himself

of the great utility of vaccination with the virus of cow-pox. At first

Jenner’s discovery met with great opposition, but his method was soon

verified in France and several other countries and it was not long

before it was generally practised.

[Sidenote: [532]]

When Pasteur set himself to study the infective diseases in their

relation to micro-organisms the idea of profiting by the discovery of

these pathogenic organisms and of drawing from them a weapon against

infections soon arose in his mind. He studied Jenner’s work in order to

extract from it any indications capable of putting him into the right

path. He induced his collaborators to carry out several series of

experiments with the object of immunising the animal organism against

infective micro-organisms. During this laborious and original work

chance[844] helped in the accomplishment of his task. When, at the

conclusion of the holidays in the autumn of 1879, Pasteur and his

collaborators Chamberland and Roux wished to resume their experiments on

fowl cholera, they found to their great surprise that the

micro-organisms of this disease, usually so fatal, had become innocuous.

Fowls, that received doses of cultures much more than sufficient to

cause death, did not experience any ill effect. Prepared by his previous

knowledge and by the continual direction of his thoughts to the

prevention of contagious diseases, Pasteur divined at once the great

bearing of this check in his inoculations with old cultures, and

immediately began to make precise experiments as to the vaccinating

power of these micro-organisms which had become innocuous. These

researches led him to the discovery of two great principles: that of the

attenuation of viruses, and that of the vaccinating property of

attenuated micro-organisms. Various memoirs by Pasteur[845] established

these laws in a very exact manner; moreover he gave all the information

necessary to allow of the principal results being controlled and

verified. In France, this great discovery was at once accepted by

various investigators, though others found occasion to manifest their

scepticism. Abroad this discovery met with very lively opposition and

this from the highest authorities, who would not recognise the

possibility either of attenuating the virus or of conferring immunity

upon animals. The anthrax bacillus can be grown for a very long time on

culture media, the potato, for example, without losing its pathogenic

power in the slightest degree. Therefore, it was said, this attenuation

of virus can have no actual existence. White rats that have resisted one

or more inoculations of the anthrax bacillus may die from a later

inoculation of the same micro-organism. Therefore there is no acquired

immunity, etc. The principles laid down by Pasteur are from every point

of view of such prime importance, that very numerous experiments were

carried out at once for the purpose of verifying their exactness and the

contest was not a long one. In the course of a few years it was

universally recognised that the attenuation of viruses, and also the

vaccination by attenuated micro-organisms, were realities which

henceforth cannot be denied and which must pass into the domain of

truths definitely acquired. An attempt was then made to extend these

fresh victories to the other infective diseases. Pasteur, Chamberland,

and Roux applied themselves to devising a method of vaccinating animals

against anthrax and against rabic virus; Pasteur and Thuillier extended

their researches on this subject to swine erysipelas. From several other

quarters the search for vaccines was instituted. Toussaint made various

attempts, at times crowned with success, to immunise animals against

anthrax by means of heated anthrax blood. Arloing, Cornevin, and Thomas

succeeded in vaccinating the Bovidae against symptomatic anthrax.

Loeffler was the first in Germany to demonstrate that rabbits which had

recovered from the disease set up by the bacillus of mouse septicaemia

acquired an immunity against the attacks of this organism. It is not

necessary to cite further examples, so numerous have they become and so

unanimously confirmatory.

[Sidenote: [533]]

After the first steps had been taken along this new path Pasteur and his

collaborators began to apply the knowledge they had gained to the

preparation of vaccines capable of giving practical results. The two

anti-anthrax vaccines and the two vaccines against swine erysipelas were

the fruit of these attempts. Here, again, numerous objections were

raised against these discoveries. Sheep which had received enormous

quantities of the bacillus may die from anthrax in spite of the two

Pasteurian vaccines and from that it was wished to conclude that these

vaccines should not be employed in practice to protect sheep against the

anthrax fever. The results of experiments made on a large scale in

various parts of the globe have demonstrated the inadequacy of these

objections and these questions are now regarded as definitely settled.

[Sidenote: [534]]

So large a number of investigations, in response to the most urgent and

immediate needs, was not favourable to minute researches on the

mechanism of this immunity which had been revealed in so marvellous a

fashion. In spite of this, Pasteur applied himself to the solution of

this problem so far as this was possible under the conditions in which

he carried on his investigations. He thought that acquired immunity was

the result of the impossibility of the growth of a pathogenic

micro-organism in a medium in which it had previously been cultivated.

When the micro-organism of fowl cholera sets up in certain individuals a

disease which though grave is not fatal, or when the attenuated

micro-organism produces a simple, transient discomfort, it lives in both

cases in the fluids and tissues of the animal. This existence is

possible in consequence of the absorption of certain nutrient

substances. Once these substances are consumed they are not easily

renewed, and in consequence the vaccinated organism becomes incapable of

nourishing the special micro-organism a second or a third time. To

support this brilliant hypothesis by precise facts Pasteur made

experiments on the conditions met with in the development of the

micro-organism of fowl cholera _in vitro_. He filtered a broth culture

of this micro-organism after it had grown luxuriantly for several days,

and into the fluid, which had now become clear and transparent, he sowed

afresh the same micro-organism. No growth took place and the fluid

remained quite clear. This absence of development might be explained

either by the presence in the fluid of some excremental substance thrown

off during the first culture or by the absence of some substance

indispensable for the nutrition of the micro-organism. Pasteur excluded

the first hypothesis by an experiment which demonstrated that it is

sufficient to add to the filtered fluid a small quantity of fresh

nutritive substances to enable the micro-organism again to develop

abundantly. It is therefore to the absence of some element essential to

the existence of the micro-organism that we must attribute the immunity

enjoyed by animals which have been vaccinated or which have undergone

spontaneous cure. This is how Pasteur[846] expressed himself on this

point: “the muscle which has been much affected has, even after healing

and repair, become in some way incapable of supporting the growth of the

micro-organism, as if the latter, by a previous culture, had eliminated

from the muscle some principle that life does not bring back and whose

absence prevents the development of the small organism. There is no

doubt that this explanation, to which the plainest facts at the moment

lead us, will become general and applicable to all the virulent

diseases.”

This explanation appeared to be a reasonable one to several observers,

amongst whom I may cite Chauveau[847], the distinguished author of

important works on viruses. “In all probability this seductive theory,”

says Chauveau, “based on one of the most interesting of those clear and

decisive experiments for which Pasteur is famous, applies to the

majority of cases of immunity acquired by protective inoculation.” But

Chauveau thinks that it does not explain natural immunity, especially

that of the Algerian sheep, against anthrax, an example that he had

studied on several occasions. When he inoculated into these animals

large quantities of anthrax bacilli, not going beyond certain limits,

the sheep resisted perfectly; but injections of enormous doses were

nearly always capable of overcoming this natural immunity of the

Algerian sheep and of inducing in them a fatal anthrax. Chauveau thinks

that this fact is best explained by the presence of an inhibitory

substance in the blood plasma, whose action becomes exhausted when

distributed over a very large number of bacilli. This opinion was not,

however, shared by Pasteur[848], who raises the objection that natural

immunity can really be produced and maintained without the presence of

this inhibitory substance from the fact that fowls, which exhibit such

marked resistance against anthrax, readily contract the disease when the

temperature of their bodies is lowered. Under these conditions it is

unimaginable that an inhibitory substance has disappeared under the

influence of cold.

[Sidenote: [535]]

The controversy existent from the birth of theories on immunity shows us

that from the very commencement the problem was found to be a very

complex one, and that to attack it in a satisfactory way we must as far

as possible multiply and deepen our study of the phenomena which

accompany the resistance of the animal against pathogenic

micro-organisms. Thus, Chauveau[849] was not long before he undertook

experiments having for their object the determination of the fate of

anthrax bacilli when injected into the blood vessels of Algerian sheep.

He found that these organisms disappeared from the blood at the end of a

few hours, but they were then to be found accumulated in the lung,

spleen, and certain other viscera. In these positions the bacilli become

incapable of reproducing themselves and in refractory individuals soon

disappear, being opposed by the inhibitory substances of the blood

plasma.

The two theories just sketched have this point in common, that they both

attribute the natural or acquired immunity to humoral and purely passive

properties. According to one theory it is the impoverishment of the

fluids of the animals which prevents the development of the pathogenic

organism, whilst according to the other it is the presence of some

bacterial poison which brings about the same result. To give

experimental support to his theory Pasteur brought forward his attempts

at sowing micro-organisms in culture media exhausted by a previous

development of the same organism, eliminating, so to say, the active

influence of the animal organism. It is true that, in order to explain

natural immunity, it was necessary to ascribe a rôle to the

“constitution” and to the “vital resistance,” interpreting this, as

Naegeli had already done, in the sense of a competition for the oxygen

and the nutritive substances between the parasites and the cells of the

body.

[Sidenote: [536]]

Adopting this point of view, Hans Buchner[850], a pupil of Naegeli,

attempted to gain a more precise idea of the conditions under which

acquired immunity against infective diseases is set up. He developed his

theory in various publications; this theory consists, briefly, in the

property of the animal organism to reinforce the local resistance of the

organs by means of an inflammatory reaction. The starting-point of this

local theory is the thesis that each pathogenic micro-organism can only

manifest its pathogenic action when it enters the particular organ in

which it is capable of living and maintaining itself. Thus, the

pneumonococcus can live in the lungs only, the cholera vibrio in the

intestines only, and so on. Every time that a pathogenic micro-organism

becomes localised in its special organ, an inflammatory action is set up

which results in the reinforcement of the living elements of the organ

in question. Inflammation, therefore, is regarded by Buchner as a

salutary reaction, which acts, not directly on the exciting morbific

cause, but through the mediation of the specific cells of the organs.

This theory of immunity led Buchner to propose arsenical treatment as a

remedy against microbial disease, because arsenic is, of all drugs, the

one capable of setting up the greatest inflammatory reaction.

Another German observer, Grawitz[851], proposes a theory of acquired

immunity, according to which a first attack of an infective disease sets

up “the adaptation of the cells to the power of energetic assimilation

of the fungi.” This reinforced adaptation is transmitted to the

descendants of the cells which have acquired it, and for that reason the

immunity may persist for months, and even years. Grawitz attempted to

base his views on experiments on the acquired immunity against the

fungus of the lily of the valley, but Loeffler[852] soon demonstrated

that this thesis could not be maintained, and that the immunity assumed

by Grawitz did not, in reality, exist.

It will be seen that all the theories summarised above are marked by

their vague character and want of precision; this is not at all

astonishing when we take into consideration the very imperfect knowledge

of the phenomena of immunity. It is evident that if we wish to gain a

satisfactory idea of the mechanism of the resistance of the animal body

against pathogenic micro-organisms, we must inform ourselves as to the

modifications which take place in the organs and tissues at the time of

the acquisition of the immunity, and also find out what becomes of the

micro-organisms in a refractory animal.

We have seen that Chauveau demonstrated that anthrax bacilli when

injected into the vessels of Algerian sheep disappear, but he was unable

to say anything as to the way in which this disappearance was brought

about in nature. Buchner accepted the reinforced resistance of inflamed

organs without being able to describe the phenomena which manifest

themselves during the inflammation of tissues invaded by the pathogenic

micro-organisms.

[Sidenote: [537]]

Independently of these theoretical and rather speculative views on

immunity, there has been an addition to our scientific assets of fairly

exact data on the relation of certain pathogenic organisms to the organs

and tissues of susceptible or refractory animals. When, as a result of

the labours of Davaine and Obermeyer, the attention of pathologists,

especially of those working at pathological histology, was drawn to the

part played by micro-organisms in infective diseases, a diligent search

was instituted for these organisms in sections of the organs of persons

who had died from various diseases. Masses of cocci especially were

found in the organs of individuals who had died from diphtheria,

puerperal fever, and various forms of pyaemia. In the course of these

investigations attention was drawn fairly frequently to the presence of

micro-organisms inside the white corpuscles of pus and of other morbid

products. Amongst the first to make this observation I may cite

Hayem[853] in France, and Birch-Hirschfeld[854], Klebs, Rindfleisch, von

Recklinghausen, and Waldeyer in Germany. Klebs[855] speaks of the

presence of micro-organisms in infected wounds, in the interior of

contractile white corpuscles, and attributes to these cells the

principal rôle in the transport of these parasites in the lymphatic

tissue. Waldeyer[856] cites a case of puerperal fever in which the

corpuscles of the peritoneal pus were filled with bacteria. Similar

observations were by no means rare; and they led to a general conclusion

that micro-organisms meet with such favourable conditions inside the

leucocytes that they would contribute to their dissemination through the

body. This opinion had become so general that when Koch[857], in frogs

inoculated with anthrax bacilli, made the discovery of round cells

containing large numbers of these micro-organisms he did not hesitate to

conclude that the bacilli found a favourable medium in the substance of

these elements. Now the frog, under ordinary conditions, is refractory

to anthrax.

[Sidenote: [538]]

As early as 1874, however, Panum[858] had given expression to the view,

in a vague fashion it is true, that leucocytes might assist in the

destruction of micro-organisms. In his memoir on putrefactive poisons we

find a note wherein occurs the following reflection: “For the solution

of the question as to how and in what situations the ordinary bacteria

of putrefaction disappear, an interesting communication made by

Birch-Hirschfeld seems to me to furnish an indication. According to this

observer the micrococci, introduced into the circulation, are deposited

in the lymphatic glands and in the spleen, after having, for the most

part, entered into the blood corpuscles. That the ordinary bacilli of

putrefaction really die in the body is proved, not only by the

circumstance that they remain inactive after the acute paroxysm of

putrid intoxication has been happily surmounted, but also by the

important observations made by Eberth on the innocuousness of the

inoculation of ordinary bacteria into the cornea.” These lines contain

the indication that the corpuscles of the blood (in this case

undoubtedly leucocytes) ingest the bacteria introduced in the blood

current and destroy them.

Some years later, in 1877, Grawitz[859], in connection with his

researches on the parasite of the lily of the valley, made the remark

that the fungi, when introduced into the blood of mammals, are seized by

the white corpuscles and thus “withdrawn from contact with the

assimilable fluid.” Gaule[860] who, as we know, sought to demonstrate

that the _Drepanidium_ of the frog’s blood is nothing but the fragments

of cell nuclei transformed into ‘Würmchen,’ has described the structure

of these organisms in the amoeboid cells of the spleen. “I happened on

one occasion,” he writes, “to observe an amoebocyte of the spleen of the

frog which in a short time ingested three ‘Würmchen,’ and then went away

briskly without leaving any trace of where it had been. Following its

movements I was able at the first to make out within the contents of the

amoebocyte the refractile body of the ‘Würmchen.’ But this body became

paler, and half-an-hour later it had been completely assimilated.”

Undoubtedly these “Würmchen” were nothing but parasites (_Drepanidium_),

and have no connection with the cell nuclei of frogs. Their ingestion,

followed by destruction, was, therefore, a defensive act on the part of

the body manifested by the amoeboid cells of the splenic pulp.

[Sidenote: [539]]

[Sidenote: [540]]

In the same year, 1881, in which this observation by Gaule was

published, Roser[861], assistant in surgery at Marburg, published a

small pamphlet on the lower animals. In this pamphlet the possibility of

growing certain unicellular organisms in urine and milk and the

adaptation of these organisms to saline solutions received special

mention. At the end of one of his paragraphs Roser expresses his views

on immunity, although this subject was not discussed at all in his

pamphlet. He expresses himself thus: “The immunity of animals and plants

in complete health depends in my opinion: (1) on the relative quantity

of salt contained in their fluids, and (2) on the property of their

contractile cells of ingesting the enemy which enters the animal body”

(p. 18). As these statements have been put forth without receiving any

further development, in the midst of all kinds of other speculations, it

is not astonishing that the words I have just quoted, as well as Roser’s

pamphlet itself, should not have attracted the attention of either

zoologists or medical men. In the reviews for these two sciences

(Schmidt’s _Jahrbücher_ and the _Zoologischer Jahresbericht_ of the

Zoological Station at Naples) it is not even mentioned. It appears that

not only did other biologists and medical men attach no importance to

Roser’s speculations, but that the author himself did not claim any

great value for them. I draw this conclusion from the fact that five

years after his first pamphlet he published a second on inflammation and

healing[862] in which he does not apply his theory of immunity to

explain these two phenomena. This new work is of an even more

speculative character than was the first, and instead of attempting to

show any relation between the anti-infective part played by the

leucocytes and their migration during inflammation, Roser insists on the

fundamental independence of this phenomenon of healing. For him the

inflammation, accompanied by diapedesis, must not be looked upon as a

healthy reaction of the body, but as a manifestation of disease. The

heat which is observed under these conditions must be attributed in part

at least to the production of heat by infective micro-organisms. I must

confess that Roser’s two pamphlets were unknown to me for many years,

and it was Hueppe who drew my attention to them by his mention of them

in the fourth edition of his work on bacteriological methods[863] which

appeared in 1889. I had then, independently of the Marburg surgeon and

by a totally different path, arrived at my conclusions as to the part

played by the amoeboid cells. At the commencement of my researches on

healing and immunity the passages cited above from the publications of

Panum, Gaule, and Grawitz were also unknown to me. Having long studied

the problem of the germinal layers in the animal series, I sought to

gain some idea of their origin and significance. The part played by the

ectoderm and the entoderm appeared quite clear, and the former might

quite reasonably be regarded as the cutaneous investment of primitive

multicellular animals, whilst the latter might be regarded as their

organ of digestion. The discovery of intracellular digestion in many of

the lower animals led me to regard this phenomenon as characteristic of

those ancestral animals from which might be derived all the known types

of the animal kingdom (excepting, of course, the Protozoa). The origin

and the part played by the mesoderm appeared the most obscure. Thus,

certain embryologists supposed that this layer corresponded to the

reproductive organs of primitive animals: others regarded it as the

prototype of the organs of locomotion. My embryological and

physiological studies on sponges led me to the conclusion that the

mesoderm must function in the hypothetically primitive animals as a mass

of digestive cells, in all points similar to those of the entoderm. This

hypothesis necessarily attracted my attention to the power of seizing

foreign corpuscles possessed by the mesodermic cells. This fact has long

been recognised. It was known that the white corpuscles of the

Vertebrata often contained various kinds of cells, especially red and

white blood corpuscles. It was known, also, that the amoeboid cells were

capable of ingesting granules of coloured substances. When making an

injection of indigo into the vessels of _Thetys_, Haeckel[864] in 1858

was surprised to find the blue granules inside the amoeboid blood

corpuscles of this beautiful gasteropod mollusk. This fact has since

been confirmed by many observers, and the capacity of the amoeboid cells

to take up foreign bodies became recognised as a general phenomenon.

Nevertheless this phenomenon was not regarded as being analogous to

digestion. Thus Haeckel[865] himself, in his researches on the

calcareous sponges, advocated the view that the foreign bodies

penetrated into the interior of the viscous protoplasm in a purely

passive fashion.

[Sidenote: [541]]

Observations that I made on sponges and on certain pelagic animals,

transparent and of simple organisation, convinced me that the presence

of foreign corpuscles in the amoeboid cells of the mesoderm must be

attributed to an active ingestion by these cells which, in every

respect, might be compared to the phenomena of intracellular digestion

in the epithelial cells of the digestive canal of many of the lower

animals. In order to demonstrate this fact clearly it was necessary to

bring forward exact experimental proof. I set myself, therefore, during

my stay at Messina in 1882 and 1883, to study the rôle of the amoeboid

cells of the mesoderm from the point of view of intracellular digestion.

I found it an easy matter to demonstrate that these elements seized

foreign bodies of very varied nature by means of their living processes,

and that certain of these bodies underwent a true digestion within the

amoeboid cells. My principal thesis, that is to say the idea of the

intimate relations between the entoderm and the mesoderm, was thus fully

confirmed.

Pondering over these results, which were quite new at the time, the idea

suggested itself to me that the digestive function, so profoundly rooted

in the mesodermic elements, must play a part in many of the vital

phenomena of animals. Starting from this standpoint, I succeeded in

demonstrating that, during the very complicated metamorphoses of

Echinoderms, such as the _Synaptae_, the amoeboid cells of the mesoderm

fulfil a function in the atrophy of numerous larval organs. I have never

prosecuted any medical studies; but some time before my departure for

Messina I listened to the reading of Cohnheim’s treatise on General

Pathology, and I was struck by his description of the facts and of his

theory of inflammation. The former, especially his description of the

diapedesis of the white corpuscles through the vessel wall, seemed to be

of momentous interest. His theory, on the other hand, appeared to be

extremely vague and nebulous. It occurred to me that a comparative study

of inflammation in lower animals of simple organisation would certainly

throw light on the very complex pathological phenomena in the

Vertebrata, even in the frog which had served as the starting-point for

Cohnheim’s remarkable experiments.

[Sidenote: [542]]

Since, in the atrophy of the larval organs of the _Synaptae_, the

essential rôle is accomplished by the amoeboid cells of the mesoderm

which accumulate and unite into masses, the richness of inflammatory

exudations in white corpuscles may perhaps signify that these corpuscles

have a very important function to fulfil. This reflection led me to make

the following experiment: to wound and introduce spines beneath the skin

of very transparent marine animals; if my hypothesis should be well

founded this should bring about an accumulation of amoeboid cells at the

injured spot. I selected for this purpose the large Bipinnaria larvae of

starfish, so abundant at Messina, and inserted prickles of the rose into

their bodies. Very shortly these prickles were found to be surrounded by

a mass of amoeboid cells such as we see in human exudation as the result

of the introduction of a spine or other foreign body. The whole process

took place under my eyes in a transparent animal possessing neither

blood nor other vessels, nor a nervous system. The first point was

settled. The inflammatory exudation must be considered as a reaction

against all kinds of lesions, the exudation being a more primitive and

more ancient phenomenon in inflammation than are the functions of the

nervous system or of the vessels.

I know quite well that, at the period when I made my researches (1882),

pathologists regarded inflammation as the consequence, if not always, at

least in the majority of cases, of the penetration of micro-organisms.

From this followed the conclusion that the diapedesis and accumulation

of white corpuscles in inflammatory diseases must be regarded as modes

of defence of the organism against micro-organisms, the leucocytes in

this struggle devouring and destroying the parasites. According to this

hypothesis the significance of inflammation at once became simple and

clear. With the object of verifying my hypothesis I began to make

experiments on the lower animals, so abundant in the Straits of Messina,

and to make myself acquainted with the results that had been obtained in

general pathology and in pathological histology. A perusal of Ziegler’s

treatise on Pathological Anatomy made it clear to me that in these

branches of medical science there had long been accumulated a great

number of observations fitted to facilitate the acceptation of the new

hypothesis on inflammation and healing. Numerous and well-established

facts on the absorption of extravasated blood, on the fate of the

coloured corpuscles in the body, on the presence of micro-organisms

inside leucocytes, etc., confirmed me in my view.

[Sidenote: [543]]

When I had got together certain information and a number of facts in

support of my hypothesis I communicated the results to my lamented

friend, Kleinenberg, at that time Professor in the University of

Messina. Both medical man and zoologist, he was well qualified to offer

a judgment upon the matter; this judgment was favourable. Sometime later

I had the great pleasure of meeting the celebrated Professor Virchow at

Messina. I imparted to him my ideas and he was kind enough to come with

me to examine my preparations of Bipinnaria larvae and other lower

animals in which I had set up the phenomena of inflammation without the

assistance of nervous or vascular systems. This eminent observer greatly

encouraged me to continue my investigations. When I explained to him my

view that the inflammatory reaction on the part of the amoeboid cells

could only be understood by accepting the hypothesis that the white

corpuscles gave chase to the micro-organisms and destroyed them, Virchow

replied that in pathology just the opposite was invariably taught. The

general opinion was that micro-organisms were certainly found inside the

leucocytes and that they made use of these cells as a means of transport

and of dissemination through the body.

[Sidenote: [544]]

During my stay at Messina my researches were limited to the lower

animals, but later I began to study inflammation and the phenomena of

infection in the Vertebrata. It was not until eight months after I had

commenced my researches in this direction that I decided to publish my

results. I first set them forth in an address given at Odessa before the

Congress of Naturalists and Medical Men in 1883. Later, they were

published in a special article inserted in Claus’s _Arbeiten_ at

Vienna[866], and in a small work which appeared in the _Biologisches

Centralblatt_[867]. I sought especially to develop the idea that the

intracellular digestion of unicellular organisms and of many

Invertebrata had been hereditarily transmitted to the higher animals and

retained in them by the amoeboid cells of mesodermic origin. These

cells, being capable of ingesting and digesting all kinds of

histological elements, may apply the same power to the destruction of

micro-organisms. In order to support this conclusion I introduced

various kinds of bacteria into the bodies of some of the lower animals

and I demonstrated that they were ingested and destroyed by the amoeboid

cells. It was evident, however, that this proof was not sufficient. I

then set myself to study the diseases of small Invertebrata sufficiently

transparent to be observed directly under the microscope. The

_Daphniae_, those small crustacea so numerous and so frequent in

fresh-water, furnished me with a favourable medium in which to study a

real struggle which takes place between their leucocytes and the spores

of a vegetable parasite belonging to the group of the Blastomycetes. In

many cases the amoeboid cells guarantee the integrity of the animal by

devouring a large number of these spores and transforming them into an

inert detritus. In other cases, on the contrary, the fungi get the upper

hand in the struggle; they succeed in germinating and in overcoming the

resistance of the leucocytes by reproducing themselves rapidly and by

killing these cells with their poisons. The history of this disease and

of this struggle was published in _Virchow’s Archiv_[868].

Some time afterwards I published in the same journal my work on the

anthrax bacillus[869], in which I attempted to demonstrate that in the

Vertebrata also the invasion of pathogenic micro-organisms sets up a

desperate struggle between them and the amoeboid cells.

In these four works I made use of the term “phagocytes” to designate the

amoeboid cells capable of seizing and digesting the micro-organisms and

other formed elements. To the theory based on this property of the

defensive cells I gave the name of “theory of phagocytes.”

I thought, as already mentioned above, that the observations on

absorption and leucocytes, which had been accumulating for years in

pathological histology, had sufficiently paved the way for a favourable

reception to the idea that the amoeboid cells are defensive elements of

the body capable of guaranteeing to it immunity and cure. In this I was

mistaken. It was precisely the specialists in this branch of science who

from the first manifested the most lively opposition to this theory.

However, in the Presidential Address delivered before the 66th meeting

of the British Association held at Liverpool in 1896, Lord Lister

said[870]: “If ever there was a romantic chapter in pathology, it has

surely been that of the story of phagocytosis.” These words encourage me

to put before the reader the essential features of this story.

[Sidenote: [545]]

My first two memoirs published in 1883 did not in any way attract the

attention of the medical public. These investigations had a character

that was too zoological to be noticed by pathologists. But the two

following publications, in which I treated of the _Daphnia_ disease and

especially of bacterial anthrax, immediately roused severe criticism.

Baumgarten[871], the well-known pathologist, opened the battle by the

publication of a review of my researches on phagocytosis. He attempted

to sap the basis of my theory, and not contented with _à priori_

arguments, he set his pupils to make a series of researches on the fate

of micro-organisms in the refractory animal. These researches resulted

in several theses for the doctor’s degree which sought to demolish every

point of the theory of phagocytosis.

Later, Baumgarten[872] published a long and above all admirably written

analytical article entitled: “Zur Kritik der Metschnikoff’schen

Phagocytentheorie,” in which, with much talent and wit, he attempted to

demolish the bases and conclusions of the phagocytic theory.

Baumgarten regards the precise observations which I had been

accumulating for some years as incorrect and refuted by the observations

and experiments of his pupils. The arguments that I give to justify my

theory are, according to the same critic, contrary to logic and to

truth. If the phagocytes are really elements destined to guarantee the

integrity of the animal organism how is it, asks Baumgarten, that just

at the moment of greatest danger, when the blood and the tissues are

invaded by the micro-organisms, the leucocytes are conspicuous by their

absence? The answer that there is no predestination in the phagocytosis,

and that the danger is the greater the more feeble the phagocytic

reaction—a fact which is in perfect harmony with the law of causes and

with the principles of the evolution of species according to Darwin’s

theory—did not satisfy my critic. He says: “If the interpretation which

Metschnikoff gives of the activity of the leucocytes appears to be

rather the product of a rich imagination than the result of the

objective observation of the seeker, it matters little that his account

of the development of the leucocyte in what he wishes to see in it

should be in conformity with the principles of the theory of evolution”

(p. 4).

[Sidenote: [546]]

I was able by numerous researches[873] to refute point by point the

objections based on the work of Baumgarten’s pupils, but that did not

prevent him from persisting in his negation. Only, commencing by writing

long articles, he contented himself, later, with denying the theory of

phagocytosis in small annual notes, appearing in his reviews of works on

bacteriology, which were unsupported either by argument or by any facts

mentioned in his abstracts.

Baumgarten’s example was followed by many other pathologists. Ziegler,

the well-known author of a text-book on pathological anatomy that has

certainly had a wider circulation than any other work, vigorously

attacked the theory of phagocytosis. As it was precisely from this

treatise that I had acquired my knowledge of the large number of facts

that had accumulated in pathological literature on the part played by

leucocytes in resorption, I was persuaded that Ziegler, who had

collected these statements, would be one of the first to recognise the

importance of phagocytosis in inflammation, healing, and immunity. But

this distinguished pathologist, in several of his publications[874],

expressed himself very vigorously against the phagocytic theory. The

intervention of these cells, according to him, must be purely accidental

and their rôle in the defence of the body against the micro-organisms

very insignificant. The better to demonstrate this thesis he caused his

pupils to undertake investigations on several infective diseases, and

these young observers all arrived at the same result, that phagocytosis

has nothing to do with the struggle of the animal against the anthrax

bacillus or against the bacillus of symptomatic anthrax. It is the less

necessary to enter into these details now because I have, in the

preceding chapters, given sufficient proofs of the incorrectness of the

objections advanced by Ziegler’s school. It has been demonstrated most

conclusively (by Lubarsch’s researches, as well as by many other works)

that in anthrax in man phagocytosis, denied by one of Ziegler’s pupils,

is most marked. It is likewise well known from the researches of Ruffer,

Leclainche and Vallée, as well as from my own observations, that in

symptomatic anthrax, in which the phagocytic reaction is denied by

another of Ziegler’s pupils, it is a very important and highly developed

feature.

[Sidenote: [547]]

The opposition emanating from another eminent pathologist, Weigert[875],

particularly impressed me, because this investigator is known not only

to be an observer of great accuracy but to possess a mind of great

imagination and generalising power. In several papers he put forward his

utmost ingenuity to demolish the phagocytic theory root and branch. He

would recognise neither the importance of phagocytosis in healing and

immunity, nor the defensive function of the giant cells. Weigert,

however, contented himself with formulating theoretical objections, and

no works directed specially against the doctrine of phagocytosis have

issued from his laboratory. It must be stated, however, that although

there has been such opposition on the part of certain of our most

eminent pathologists, others amongst them have, from the beginning,

expressed themselves in more favourable terms. Thus, Virchow[876], in an

introductory article in the 101st volume of his _Archiv_, continued his

friendly attitude with regard to the works on phagocytic defence and

spoke of them as opening up a new field of research. Ribbert[877], in a

series of publications, maintained the importance of the phagocytes in

the resistance offered by the animal to the aggression of

micro-organisms, and pointed out, especially in connection with the

diseases set up by the staphylococci, the frequency of the ingestion of

these parasites by the leucocytes. He insists specially on a

modification of the phagocytic reaction, which consists in the

accumulation of white corpuscles around the centre of microbial

infection. In these cases, without the occurrence of any real ingestion

of the micro-organisms into the substance of the phagocytes, these

organisms may have their morbific manifestation hindered by the

assemblage of the white corpuscles. It is needless to insist that this

act, which I referred to in my first work in 1883, constitutes the

prelude to a true phagocytosis and is closely bound up with this

defensive phenomenon. Another pathologist, Hess[878], supports the

theory of phagocytosis by confirmatory researches of great value.

[Sidenote: [548]]

The pathologists who were adversaries of the phagocytic theory combined

their efforts to demolish it, without troubling themselves to replace it

by any other theory of defence on the part of the body which might more

easily be made to accord with their principles and their statements.

Baumgarten certainly tried to prove that micro-organisms perish in cases

where immunity is produced or healing occurs, not as the result of the

phagocytic reaction or of any other manifestation on the part of the

menaced animal, but simply “of themselves” (von selbst), that is to say,

they have simply accomplished the normal cycle of their existence and

die a natural death, this bringing about healing and immunity. As may be

readily understood he was unable to bring forward the slightest evidence

of the correctness of this hypothesis, which, I believe, has never been

accepted by anyone, nor even been defended by its author. In this

respect the attacks directed against the theory of phagocytosis by

bacteriologists have been of a very different character. Not content

with overturning this hypothesis, these observers have sought to build

upon its ruins new theories capable of offering a better explanation of

the phenomena of immunity. I must here confess at the outset that these

attacks have been much more important than those coming from the

pathologists and pathological anatomists, and have led to discoveries of

the greatest value.