_THE QUESTION OF IMMUNITY AND ANTITOXINS_
The term _natural immunity_ is used to denote natural resistance to
some particular specific disease. It may refer to race, or age, or
individual idiosyncrasies. We not infrequently meet with examples of
this freedom from disease. Certain races of men do not, as a rule, take
certain diseases. For example, plague and leprosy, though endemic in
some countries, fail to get a footing in England. This, of course, is
due in great measure to the sanitary organisation and cleanly customs
of the English people. Still, it is also due to the fact that the
English appear in some degree to be immune. Some authorities hold that
the immunity against leprosy is due to the fact that the disease has
exhausted itself in the English race. However that may be, we know that
immunity, entire or partial, exists. Children, again, are susceptible
to certain diseases and insusceptible to certain others to which older
people are susceptible. We know, too, that some individuals have a
marked protection against some diseases. Some people coming into the
way of infection at once fall victims to the disease, whilst others
appear to be proof against it. It is only in recent times that any
very intelligent explanations have been offered to account for this
phenomenon. The most recent of these, and that which appears to have
most to substantiate it, is known as immunity due to _antitoxins_.
_The products of bacteria_ are chiefly six:
1. _Pigment._ We have already seen how many organisms exhibit their
energy in the formation of many coloured pigments. They are, as a rule,
"innocent" microbes. Oxygen is required for some, darkness for others,
and they all vary according to the medium upon which they are growing.
Red milk, yellow milk, and green pus afford examples of pigment
produced by bacteria.
2. _Gas._ Quite a number of the common bacteria, like _Bacillus
coli_, produce gas in their growth; hydrogen (H), carbonic acid
(CO_{2}), methane (CH_{4}), and even nitrogen (N) being formed by
different bacteria. Many gases produced during fermentative processes
are the result, not directly of the growth of the bacillus causing
the fermentation, but indirectly owing to the splitting up of the
fermenting fluids.
3. _Acids._ Lactic, acetic, butyric, etc., are common types of acids
resulting from the growth of bacteria.
4. _Liquefying Ferment._ As we have seen, bacteria may be classified
with regard to their behaviour in gelatine medium, whether or not they
produce a peptonising ferment which liquefies the gelatine.
5. _Phosphorescence._ Some species of bacteria in sea-water possess the
power of producing light.
6. _Organic Chemical Products._ When a pathogenic bacillus grows
either in the body or in a test-tube, it produces as a result of its
metabolism certain poisonous substances called _toxins_. These may
occur in the blood as a direct result of the life of the bacillus, or
they may occur as the result of a ferment produced by the bacillus.
They are of various kinds according to the various diseases, and
by their effect upon the blood and body tissues they cause the
symptoms of the disease in question. We know, for instance, that a
characteristic symptom common to many diseases is fever. Now, fever
is produced by the action of the albumoses (bodies allied to the
proteids) upon the heat-regulating centres in the brain. Whenever we
get a bacillus growing in the body which has the power of producing a
toxin albumose, we get fever as a result of that product acting upon
the brain. Albumoses, as a matter of fact, cause a number of symptoms
and poisonous effects, but the mention of one as an illustration will
suffice. Toxins act, roughly speaking, in two ways:
(1) They have a local action, as, for example, in the formation of an
abscess. The presence of the causal bacteria in the tissue brings about
very marked changes. There is a multiplication of connective-tissue
corpuscles, an emigration of leucocytic cells, a congestion of blood
corpuscles. All these elements assist in creating a swelling and
redness, and pain by the subsequent pressure upon the delicate nerve
endings. These, as we all know, are the symptoms of a "gathering"
or abscess. It is a "gathering" in a strict pathological sense--a
gathering of cells to oust the intruder or build around it a wall or
capsule as a protective measure. Now the toxin will commence its local
action. The oldest cells in the mass of congestion will be caused
to break down into liquid; what is called a _necrosis_, or death,
will rapidly set in; and we shall have the connective-tissue cells,
leucocytes, blood corpuscles, etc., losing their form and function, and
"coming to a point" as matter, or _pus_. The local breaking down of
these gatherings of cells into fluid matter is believed to be the work,
not of the bacteria themselves, but of their toxins.
(2) Toxins may be absorbed and distributed generally throughout the
body. They produce degenerative changes in muscles, in organs, and in
the blood itself. Let us take diphtheria as an example. The bacillus
occurs in a false membrane in the throat and occasionally other parts.
It causes first the inflammatory condition giving rise to the membrane,
and then it breaks it down. In the body of the membrane the bacillus
appears to secrete a ferment which by its action and interaction with
the body cells and proteids, chiefly those of the spleen, produces
_albumoses_ and an _organic acid_. These latter bodies are the toxins.
They are absorbed, and pass throughout the body. There are albumoses,
therefore we get the frequent pulse and high temperature of fever; the
toxins irritate the mucous membrane of the intestine, and cause various
fermentative changes in the contents of the intestine, therefore we
get the symptoms of diarrhœa; they penetrate the liver, spleen, and
kidney, therefore we get fatty degeneration and its results in these
organs; they finally affect many of the motor and sensory nerves,
breaking up their axis cylinders into globules, and therefore we get
the characteristic paralysis. Loss of weight naturally follows many of
these degenerative or wasting changes. Here, then, we have some of the
chief changes set up by the toxins, and these changes constitute the
leading symptoms in the disease as it is known clinically.
In addition to the presence of the specific bacillus in the membrane,
we also have a number of other organisms, like the _Bacillus coli_,
_Coccus Brissou_, _Streptococcus pyogenes_, and various staphylococci,
diplococci, etc. Each of these produces or endeavours in the midst
of keen competition and strife to produce, its own specific effect.
Thus we obtain the complications of diphtheria, for example various
suppurative and septic conditions. The whole of this compound process
we may tabulate roughly as follows[77]:
| BACILLUS OF DIPHTHERIA = primary infective
_Bacillus coli._ | | agent.
_Coccus Brissou._ | Inflammatory changes and fibrinous exudation.
Staphylococci. | |
Diplococci. | FERMENT IN MEMBRANE = secondary infective
Streptococci. | | agent.
| | Passes through body, and
Toxins. | by digestion of proteids
| | produces { ALBUMOSES:
Suppurative glands, | { AN ORGANIC ACID.
septic poisoning, | |
etc. | 1. Fever.
| 2. Diarrhœa.
| 3. Loss of body weight.
| 4. Fatty degeneration.
| 5. Degeneration of
| peripheral nerves, and
| resulting paralysis.
Such is the general effect of toxins in diphtheria. The same principles
apply with equal force in tetanus, typhoid, etc., the only differences
being in degree of virulence, mode of onset, and portions of the body
chiefly affected.
Sidney Martin has recently[78] elaborated the views announced by
him in 1892, and it is right that reference should be made to his
new classification of bacterial poisons. This may be represented as
follows:--
1. The poisons secreted by the bacterium itself }
= (ferment? toxin?) }
2. Products of digestive action of bacterium = } = Extracellular
albumoses: } bacterial poisons.
3. Final non-proteid products = animal alkaloid; }
4. Poisons present in the bodies of the bacillus = Intracellular
bacterial poisons.
The poisons of bacteria are, according to Sidney Martin, of a kind
which cannot be fully expressed chemically, but only pathologically.
They may be of a ferment nature in diphtheria and tetanus. The
arguments in support of that view are--(1) that they act in
infinitesimal doses, (2) that they may act slowly and produce death
after many days by profoundly affecting the general nutrition, and (3)
that they are sensitive to the action of heat in a way that no chemical
poisons are known to be. If they are considered as ferments, they must
be substances which have a peculiar affinity for certain tissues of
the body on which they produce their special toxic effect. As for the
products of digestion, they are formed either by the bacillus ingesting
the proteid and discharging it as albumose, or the digestion occurs
by means of a ferment secreted by the bacillus in the body of an
individual or animal suffering from the disease.
Sidney Martin suggests that _anthrax_ produces albumoses and an
alkaloidal substance, the former producing fever, the latter stupor.
In _tetanus_ the bacillus produces a secretion of the bacillus which
causes the convulsions. The albumoses present in this disease are
probably due to the secretory toxin. In _diphtheria_, too, we have a
secretory poison in the membrane and in the tissues, and an albumose
which is possibly the result of the secretion. It will be seen that
these views differ in some particulars from those to which we have
already referred.
However the details of the _modus operandi_ of the formation of toxins
are finally settled, we know that there comes a time when the disease
symptoms vanish, the disease declines, and the patient recovers.
Many of the older schools of medicine explained this satisfactory
phenomenon by saying that this disease exhausted itself after having
"gone through" the body. In a sense that idea is probably true; but
recently a large number of investigators have applied themselves to
this problem, and with some promising results.
Various protective inoculations against anthrax were practised as early
as 1881, and the protected animals remained healthy. In 1887 Wooldridge
succeeded in protecting rabbits from anthrax by a new method, by which
he showed that the growth of the anthrax bacillus in special culture
fluids gave rise to a substance which, when inoculated, conferred
immunity. In 1889 and 1890 Hankin and Ogata worked at the subject,
and announced the discovery in the blood of animals which had died of
anthrax of some substances which appeared to have an antagonistic and
neutralising effect upon the toxins of anthrax and upon the anthrax
bacilli themselves. These substances, they afterwards found, were
products of the anthrax bacillus. Behring and Kitasato arrived at
much the same results for tetanus and diphtheria. The next step was
to isolate these substances, and, separating them from the blood,
investigate still further their constitution. A number of workers
were soon occupied at this task, and since 1891 Buchner, Hankin, the
Klemperers, Roux, Sidney Martin, and others have added to our knowledge
respecting these toxin-opposing bodies known as _antitoxins_. In
diphtheria, as we have seen, the toxins turned out to be soluble bodies
allied to the proteids, albumoses, and an organic acid. Then arose the
question of the source of antitoxins. Some believed they were a kind
of ultratoxin--bodies of which an early form was a toxin; others held
that, as the toxins were products of the bacteria invading the tissues,
the antitoxins were of the nature of ferments produced by the resisting
tissues. Finally, they came to be looked upon as protective substances
produced _in the body cells_ as a result of toxin action, and held in
solution in the blood, and there and elsewhere exerting their influence
in opposition to the toxins.[79] The progress of disease is therefore a
struggle between the toxins and the antitoxins: when the toxins are in
the ascendency we get an increase of the disease; when the antitoxins
are in the ascendency we get a diminution of disease. If the toxins
triumph, the result is death; if the antitoxins and resistance of the
tissues triumph, the result is recovery.
We may now consider shortly how these new facts were received and
what theories of explanation were put forward to explain continued
insusceptibility to disease. It had of course been known for a
long time past that one attack of small-pox, for example, in some
degree protected the individual from a subsequent attack of the same
disease. To that experience it was now necessary to add a large mass
of experimental evidence with regard to toxins and antitoxins. The
theories of immunity were as follows:
1. _The Exhaustion Theory._ The supporters of this idea argued that
bacteria of disease circulating in the body exhausted the body of the
supply of some substance or condition necessary for the growth and
development of their own species.
2. _The Retention Theory._ It was surmised that there were certain
products of micro-organisms of disease retained in the body after an
attack which acted antagonistically to the further growth in the body
of that same species.
3. _The Acquired Tolerance Theory._ Some have advanced the theory
that, after a certain time, the human tissues acquired such a degree
of tolerance to the specific bacteria or their specific products
that no result followed their action in the body. The tissues become
acclimatised to the disease.
4. _The Phagocyte Theory._ This theory, which gained so many adherents
when first promulgated by Metschnikoff, attributes to certain cells
in the tissues the powers of "scavenging," overtaking germs of
disease, and absorbing them into their own protoplasm. This, indeed,
may be actually witnessed, and had been observed before the time
of Metschnikoff. But it was he who applied it to disease. He came
to the conclusion that the successful resistance which an animal
offered to bacteria depended upon the activity of these scavenging
cells, or _phagocytes_. These cells are derived from various cellular
elements normally present in the body: leucocytes, endothelial cells,
connective-tissue corpuscles, and any and all cells in the body which
possess the power of ingesting bacteria. If they are present in large
numbers and active, the animal is insusceptible to certain diseases; if
they are few and inactive, the animal is susceptible.
It appears that the bacteria or other foreign bodies in the blood
which are attacked by the phagocyte become assimilated until they are
a part of the phagocyte itself. Metschnikoff explained also how it
comes to pass that the phagocyte is able to encounter bacteria when
both are circulating through the blood. It is guided in this attack
upon the organisms by a power termed _chemiotaxis_. The bacteria
elaborate a chemical substance which attracts the phagocyte, and
this is termed "positive chemiotaxis."[80] But it may occur that the
chemical substance produced by the bacteria may have an opposite, or
repellent, effect upon the leucocytes, in which case we have "negative
chemiotaxis."[81] It is not to be wondered at that such a theory of
immunity based upon microscopical observations, should at first have
been widely accepted, and there can be no doubt that Metschnikoff
has collected a considerable mass of evidence in support of a theory
of phagocytosis. But when it came to be known that blood serum, from
which all leucocytes (phagocytes) had been removed, possessed the
same immunising effect as before, it was clear that such effect was
a property of the serum _per se_, and not only or wholly due to the
scavenging power of certain cells in it. Even the phagocyte theory
depends largely for its validity upon chemiotaxis, which latter was a
property of the products of the bacteria contained in the blood serum.
5. _The Antitoxin Theory._ We have gathered, then, that whenever
bacteria, introduced into the blood and tissues, fail to multiply or
produce infection (as in saprophytic bacteria, or in immunity of a
particular animal from a specific microbe), this inability to perform
their rôle is brought about by some property in the living and normal
blood serum which opposes their life and action; and further we have
learned that this protective property is exhaustible according to the
number of bacteria, and differs with various species of bacteria, and
in different animals. Buchner designates these protective bodies, held
in solution in the blood, _alexines_, and regards them as belonging
to the albuminous bodies of the lymph and plasma. Where the blood
and tissues do not possess this power, the animal is susceptible.
Now, as we have already seen from the experiments of Ogata, Kitasato,
and others, the blood of an animal dead of anthrax is protective
against anthrax, from which and the foregoing it appears that microbes
produce by their growth in the tissues poisonous substances we term
_toxins_, which have the power of producing in the blood and body
cells substances inimical to themselves, named _antitoxins_, and so
long as these latter substances remain in the tissues the body remains
insusceptible to further attacks of the same disease. Alexines are
_naturally_ produced antitoxins; antitoxins are _acquired_ alexines.
Hence we have the well-known terms "natural" and "acquired immunity."
Of the former we have already spoken. _Acquired immunity_ is a
protection not belonging to the tissues of individuals naturally and as
part of their constitution, but it is acquired during their lives as a
further accomplishment, so to speak, of their tissues. This may happen
in one or both of two ways. Either it may be an involuntary acquired
immunity, or a voluntary acquired immunity. For example, the former is
at once illustrated by an attack of the disease.
Small-pox, typhoid fever, even scarlet fever, are diseases which very
rarely attack the same individual twice. That is because each of these
diseases leaves behind it, on its first appearance, its antitoxic
influence. Hence the individual has _involuntarily_ acquired immunity
against these diseases. An example of voluntary acquired immunity
is also at hand in the old method of preventive inoculation for
small-pox, or _variolation_. This was clearly an inoculation setting
up an artificial and mild attack of small-pox, by which the antitoxins
of that disease were produced, and protected the individual against
further infection of small-pox; that is to say, it was a voluntary
acquired immunity. This form of artificial production of protection is
generally called _artificial immunity_. Let us now marshal together
these various terms in a table as follows:
_Immunity_ in man {= a condition of protection of insusceptibility to
{ certain diseases.
1. _Natural immunity_ = constitutional protection produced by
_alexines_.
2. _Acquired immunity_
{ _Acquired naturally_ (involuntarily) produced by antitoxins formed
{ byan attack of the disease.
{
{ _Acquired artificially_ (voluntary)=
{
{ (_a_) _Active_ immunity, produced by direct inoculation of the
{ weakened bacteria or weakened toxins of the disease,
= { _e. g._, vaccination, or Pasteur's treatment of rabies,
{ or Haffkine's inoculation for cholera.
{
{ (_b_) _Passive_ immunity, produced by inoculation, not of the
{ disease or of its toxins, but of the _antitoxins_
{ produced in the body of an animal suffering from the
{ specific disease.
It is hoped that previous remarks will have explained the meaning of
the terms used in the above table, with the exception of the last two
phrases of active and passive immunity. We propose now to consider in
some detail the four illustrations quoted under these two headings,
viz., vaccination, Pasteur's treatment of rabies, anti-cholera
inoculation, and antitoxin inoculation. From all accounts, it is to be
feared that these four phases of artificial immunity are hopelessly
confused in the educated public mind. Nor is this to be wondered at
when we reflect upon the rapid growth of the whole science of immunity,
and upon the ever-varying forms of nomenclature through which it has
passed.
_Vaccination for Small-pox._ In 1717 Lady Mary Wortley Montagu[82]
described the inoculation of small-pox as she had seen it practised
in Constantinople. So greatly was she impressed with the efficacy of
this process that she had her own son inoculated there, and in 1721 Mr.
Maitland, a surgeon, inoculated her daughter in London. This was the
first time inoculation was openly practised in England.[83] For one
hundred and twenty years small-pox inoculation (or _variolation_, as
it is more correctly termed) was practised in England, until by Act of
Parliament in 1840 it was prohibited.
There were different ways of performing variolation, but the most
approved method was similar to the modern system of arm-to-arm
vaccination, the arm being inoculated with a lancet in one or more
places with small-pox lymph instead of, as now, with vaccine lymph.
As a rule, only local results or a mild attack of small-pox followed,
which prevented an attack of natural small-pox. Its disadvantage is
apparent on the surface. It was a means of breeding small-pox, for the
inoculated cases were liable to create fresh centres of infection. In
1796 Edward Jenner, who was a country practitioner in Gloucestershire,
observed that those persons affected with cow-pox, contracted in the
discharge of their duty as milkers, did not contract small-pox, even
when placed in risk of infection. Hence he inferred that inoculation of
this mild and non-infectious disease would be preferable to the process
of variolation then so widely adopted in England. Jenner therefore
suggested the substitution of cow-pox lymph (vaccine) in place of
small-pox lymph, as in ordinary variolation.
It should not be forgotten that variolation was thus the first work
done in this country in producing artificial immunity, and was followed
by vaccination, which was only partly understood. Even to-day there is
probably much to learn respecting it. Both variolation and vaccination
may be described as _active immunisation by means of an attenuated form
of the specific virus causing the disease_. The nature of the specific
virus of both small-pox and cow-pox awaits discovery. Burdon Sanderson,
Crookshank, Klein, and Copeman have all demonstrated bacteria in
cow-pox or vaccine lymph, and in 1898 Copeman announced that he had
isolated a specific bacillus and grown it upon artificial media.[84]
Numerous statements have been made to the effect that a specific
bacillus has been found in small-pox also. But neither in small-pox nor
cow-pox is the nature of the contagion really known.[85]
These facts, however, do not remove the suspicion which has hitherto
rested upon vaccine lymph as a vehicle for bacteria of other diseases
which by its inoculation may thus be contracted. A few remarks
are therefore called for at this juncture upon the recent work of
Dr. Monckton Copeman and Dr. Frank Blaxall in respect to what is
known as _glycerinated calf lymph_. Evidence has been forthcoming
to substantiate in some measure the distrust which many of the
public have from time to time felt in the vaccine commonly used in
vaccination, hence the new form as above designated. This retains the
toxic qualities required for immunity, but is so produced that it
possesses in addition three very important advantages; namely, it is
entirely free from extraneous organisms, it is available for a large
number of vaccinations, and it retains full activity for eight months.
It is prepared as follows:
A calf, aged three to six months, is kept in quarantine for a week. If
then found upon examination to be quite healthy, it is removed to the
vaccination station, and the lower part of its abdomen antiseptically
cleaned. The animal is now vaccinated upon this sterilised area with
glycerinated calf lymph. After five days the part is again thoroughly
washed, and the contents of the vesicle, which have of course
appeared in the interval, are removed with a sterilised sharp spoon,
and transferred to a sterilised bottle. This is now removed to the
laboratory, and the exact weight of the material ascertained. A calf
thus vaccinated will yield from 18 to 24 grams of vaccine material.
This is now thoroughly triturated and mixed with six times its weight
of a sterilised solution of 50 per cent. chemically pure glycerine
in distilled water. The resulting emulsion is aseptically stored in
sealed tubes in a cool place. For four weeks it is carefully examined
bacteriologically until the glycerine has absolutely killed any
possible germ that may have obtained entrance. When by agar plates it
is demonstrably sterile it is ready for distribution.
_Pasteur's Treatment of Rabies._ Rabies is a disease affecting dogs (in
Western Europe) and wolves (in Russia), and can be transmitted to other
animals and man, infection being carried by the bite of a rabid animal.
It takes two chief forms: (1) furious rabies and (2) paralytic rabies.
The former is more common in dogs. The animal becomes restless, has a
high-toned bark, and snaps at various objects. Sometimes it exhibits
depraved appetite; spasms of the throat follow, and these soon develop
into convulsions, which are followed by coma and death. In man the
incubation period is fortunately a very long one, averaging about forty
days. Nervous irritability is the first sign; spasms occur in the
respiratory and masticatory muscles, and the termination is similar to
rabies in the dog. The symptom of fear of water is a herald of coming
fatality.
Although a number of the workers at the Pasteur Institute and elsewhere
have addressed themselves to the detection of a specific microbe, none
has as yet been found, although, in the opinion of Pasteur, such an
agent may be suspected as the cause.
Pathologically rabies and tetanus (see page 168) are closely allied
diseases, and the recent remarkable additions to our knowledge of the
latter disease only make the similarity more evident. There are in
rabies three chief sets of _post-mortem_ signs. First, and by far the
most important, are the changes in the nervous system. Here we find
patches of congestion in the brain, and breaking down of the axis
cylinders of the nerves. The stomach, in the second place, exhibits
hæmorrhagic changes, not unlike acute for arsenical poisoning. Thirdly,
the salivary glands show a degenerative change in a breaking down of
their secreting cells. Roux has pointed out that in life the saliva
of a mad dog becomes virulent three days before the appearance of the
symptoms of disease.
We may now turn to the method of treatment which was introduced by
Pasteur. Before his time cauterisation of the wound was the only
means adopted. If more than half an hour has elapsed since the bite,
cauterisation is of little or no avail. The basis for Pasteur's
treatment was the difference in virulence obtainable in spinal cords
infected with rabies. Pasteur found that drying the cord led to a
lessening of its virulence, just as certain other conditions increased
its virulence. Next he established the fact that subcutaneous injection
of a weak virus, followed up with doses of ever-increasingly virulent
cords, immunised dogs against infection or inoculation of fully
virulent material. From this he reasoned that if he could establish
a standard of weakened virulence he would have at hand the necessary
"vaccine" for the treatment of the disease.
[Illustration: SUSPENDED SPINAL CORD
In drying jar containing Calcium Chloride]
Subsequent research and skilled technique resulted in a method of
securing this standard, which he found to be a spinal cord dried for
fourteen days. The exact details are as follows: The spinal cords
of two rabbits dead of rabies are removed from the spinal canal in
their entirety by means of snipping the transverse processes of
the vertebrae. Each cord is divided into three more or less equal
pieces, and each piece, being snared by a thread of sterilised silk,
is carefully suspended in a sterilised glass jar. At the bottom of
the jar is a layer, about half an inch deep, of sterilised calcium
chloride. The jars are then removed to a dark chamber, where they are
placed at a temperature of 20-22° C. in wooden cases. Here they are
left to dry. Above each case is a tube of broth, to which has been
added a small piece of the corresponding cord, in order to test for
any organismal element that may by chance be included. In case of the
slightest turbidity in the broth, the cord is rejected. Fourteen series
of cords are thus suspended on fourteen consecutive days. The first,
second, and third are found to be of practically equal virulence,
but from the third to the fourteenth the virulence proportionately
decreases, and on the fifteenth day the cord would be practically
innocuous and non-virulent. When treatment is to be commenced,
obviously the weakest--that is, the fourteenth day--cord is used to
make the "vaccine," and so on in steadily increasing doses (as regards
virulence) up to and including a third-day cord. The fourteenth-day
cord is therefore taken, and a small piece cut off and macerated in 10
cc. of sterile broth, which are placed in a conical glass and covered
with two layers of thick filter-paper, the glass with its covering
having been previously sterilised by dry heat. When the patient bitten
by the rabid animal is prepared, 3 cc. of this broth emulsion of spinal
cord are inoculated by means of a hypodermic needle into the flanks
or abdominal wall. On the following day the patient returns for an
inoculation of a cord of the thirteenth day, and so on until a rabid
cord emulsion of the first three days has been inoculated. As a matter
of practice, the dosage depends upon the three recognised classes of
bites, viz. (1) bites through clothing (least severe); (2) bites on the
bare skin of the hand; (3) bites upon the face or head, most severe
owing to the vascularity of these parts. An example of each, which the
writer was permitted to take in the Pasteur Institute, may be here
added to make quite clear the entire practice. (See page 258.)
It may be well to add the returns of inoculation made at the Pasteur
Institute, Rue Dutot, Paris, as above described. They are as follows:
No. of Persons No. of Rate of
Year. inoculated. Deaths. Mortality.
1886 2,671 25 0.94
1887 1,770 14 0.79
1888 1,622 9 0.55
1889 1,830 7 0.38
1890 1,540 5 0.32
1891 1,559 4 0.25
1892 1,790 4 0.22
1893 1,648 6 0.36
1894 1,387 7 0.50
1895 1,520 2 0.13
1896 1,308 4 0.30
1897 1,521 6 0.39
Pasteur's treatment of rabies by inoculation of emulsions of dried
spinal cord is, therefore, a "vaccination" of attenuated virus,
resulting in antitoxin formation, to the further protection of the
individual against rabies.
One further example of the modern application of the principles of
active acquired immunity may be shortly mentioned. We refer to the
cholera and plague vaccinations. The vaccination in small-pox is an
inoculation of the _virus of the disease_; the rabies inoculation is
a transmission of the _vital products of the disease attenuated_; the
plague and cholera vaccinations are inoculations of _pure cultures of
living virus_ from outside the body. Inoculating cholera virus against
cholera has been made illegal, as variolation was in 1840. But Haffkine
has prepared two vaccines. The weak one is made from pure cultures of
Koch's spirillum of Asiatic cholera, attenuated by growth to several
generations on agar or broth at 39°C. The strong one is from similar
culture the virulence of which has been increased. One cubic centimetre
of the first vaccine is injected hypodermically into the flank, and
the second vaccine three or four days afterwards. The immunisation is
prophylactic, not remedial, and its action takes effect five or six
days after the second vaccine has been injected.
INOCULATION TREATMENT FOR PERSONS AFFECTED WITH RABIES
------------------------------
1. FOR THOSE BITTEN THROUGH
CLOTHES.
-------------+--------+-------
Days of |Doses of|Dates
Treatment. |Emulsion|of Cord
|per cc. |Drying.
-------------+--------+-------
1 at 11 A.M.| 3 | 14
1 " " | 3 | 13
2 " " | 3 | 12
2 " " | 3 | 11
3 " " | 3 | 10
3 " " | 3 | 9
4 " " | 3 | 8
4 " " | 3 | 7
5 " " | 3 | 6
5 " " | 3 | 6
6 " " | 3 | 5
7 " " | 3 | 5
8 " " | 3 | 4
9 " " | 2 | 3
10 " " | 3 | 5
11 " " | 3 | 5
12 " " | 3 | 4
13 " " | 3 | 4
14 " " | 3 | 3
15 " " | 3 | 3
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
-------------+--------+-------
2. FOR THOSE BITTEN ON
UNCOVERED SKIN OF HANDS,
ETC.
-------------+--------+-------
Days of |Doses of|Dates
Treatment. |Emulsion|of Cord
|per cc. |Drying.
-------------+--------+-------
1 at 11 A.M.| 3 | 14
1 " " | 3 | 13
2 " " | 3 | 12
2 " " | 3 | 11
3 " " | 3 | 10
3 " " | 3 | 9
4 " " | 3 | 8
4 " " | 3 | 7
5 " " | 3 | 6
5 " " | 3 | 6
6 " " | 3 | 5
7 " " | 3 | 5
8 " " | 3 | 4
9 " " | 2 | 3
10 " " | 3 | 5
11 " " | 3 | 5
12 " " | 3 | 4
13 " " | 3 | 4
14 " " | 3 | 3
15 " " | 3 | 3
16 " " | 3 | 5
17 " " | 3 | 4
18 " " | 3 | 3
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
... | ... | ...
-------------+--------+-------
3. FOR THOSE BITTEN ON FACE
OR HEAD.
-------------+--------+-------
Days of |Doses of|Dates
Treatment. |Emulsion|of Cord
|per cc. |Drying.
-------------+--------+-------
1 at 11 A.M.| 3 | 14
1 " " | 3 | 13
1 at 3 P.M.| 3 | 12
1 " " | 3 | 11
2 at 11 A.M.| 3 | 10
2 " " | 3 | 9
2 at 3 P.M.| 3 | 8
2 " " | 3 | 7
3 at 11 A.M.| 3 | 6
3 " " | 3 | 6
4 " " | 3 | 5
5 " " | 3 | 5
6 " " | 3 | 4
7 " " | 2 | 3
8 " " | 3 | 4
9 " " | 3 | 3
10 " " | 3 | 5
11 " " | 3 | 5
12 " " | 3 | 4
13 " " | 3 | 4
14 " " | 3 | 3
15 " " | 3 | 3
16 " " | 3 | 5
17 " " | 3 | 4
18 " " | 3 | 3
19 " " | 3 | 5
20 " " | 3 | 4
21 " " | 3 | 3
-------------+--------+-------
In plague the same plan has been followed. Luxurious crops of
Kitasato's plague bacillus are grown on ordinary nutritive media plus
large quantities of fat. The fat of milk, as clarified butter, is that
generally used. Under the globules of fat flakes of culture grow like
stalactites, hanging down into the clear broth. These are in time
shaken to the bottom, and a second crop grows on the under-surface
of the fat. In the course of a month perhaps half a dozen such crops
are obtained and shaken down into the fluid, until the latter assumes
an opaque milky appearance. This is now, unlike the cholera vaccine,
exposed to a temperature of 70° C., by which the microbes are killed.
The culture contains all the toxins, and the dose is 3 cc. This
preparation has the advantage of being easily prepared, obtainable
in large quantities, and requires no animals in its preparation.
When inoculated it produces local pain and swelling at the site of
inoculation, and general reactive symptoms such as fever. From a
careful analysis of the results of this inoculation, it is shown that
the efficacy of the prophylactic depends upon the virulence of the
bacillus culture from which the vaccine is prepared, and upon its dose
and ability to produce a well-marked febrile reaction. It appears to be
more effective in the prevention of deaths than of attacks.
The anti-typhoid vaccination is another example of inoculation to
secure active immunity. It is needless, perhaps, to point out that all
these vaccinations, except rabies, are prophylactic, and not curative.
_Passive Immunity; Preparation of Antitoxins._ We must now consider
the question of passive immunity. This, it will be remembered, may
be defined as a protection (against a bacterial disease) produced by
inoculation, not of the disease itself, as in small-pox inoculation,
nor yet of its weakened toxins, as in rabies, but of the _antitoxins_
produced in the body of an animal suffering from that particular
disease. Examples of this treatment are increasing every year, and the
term "antitoxin" has now become almost a household word. The chief
examples are to be found in diphtheria, tetanus, streptococcus, and
pneumococcus.
To be of value, antitoxins must be used as early as possible, before
tissue change has occurred and before the toxins have, so to speak,
got the upper hand. When the toxins are in the ascendency the patient
suffers more and more acutely, and may succumb before there has been
time for the formation in his own body of the antitoxins. If he can
be tided over the "crisis," theoretically all will be well, because
then his own antitoxin will eventually gain the upper hand. But in the
meantime, before that condition of affairs, the only way is to inject
antitoxins prepared in some animal's tissues whose disease began at an
earlier date, and thus _add_ antitoxins to the blood of our patient,
early in the disease, and the earlier the better, for, however soon
this is done, it is obvious that the toxins begin their work earlier
still. It should not be necessary to add that general treatment must
also be continued, and indeed local germicidal treatment, _e. g._, of
the throat in diphtheria and the poisoned wound in tetanus. Further,
in a mixed infection, as in glandular abscesses with diphtheria, it
must be borne in mind that the antitoxin is specific and may therefore
probably fail in such mixed cases.
After these preliminary remarks we will now consider shortly some of
the methods employed for the production of antitoxins. An animal is
required from whose body a considerable quantity of blood can be drawn
without injurious effect. Moreover, it must be an animal that can stand
an attack of such diseases as diphtheria and tetanus. Such an animal is
the horse. Now, by injecting into the horse (_a_) living organisms of
the specific disease, but in non-fatal doses, or (_b_) dead cultures,
or (_c_) filtered cultures containing no bacteria and only the toxins,
we are able to produce in the blood of the horse first the toxins and
then the antitoxins of the disease in question. The non-poisonous
doses of living organisms can be weakened, or, as we say, attenuated,
by various means. Dead cultures have not been much used to produce
immunity except by Pfeiffer. In actual practice the third method is
much the most general, viz., filtering a fluid culture free from the
bacteria, and then inoculating this in ever-increasing doses. The
preparation of diphtheria antitoxin may be taken as an example, but
what follows would be equally applicable to other diseases, such as
tetanus.
1. _To Obtain the Toxin._ First grow a pure culture of the
Klebs-Löffler bacillus of diphtheria in large flasks containing
"Löffler's medium," or a solution made by mixing three parts of blood
serum with one of beef broth and adding one per cent. of common salt
(Na Cl) and one per cent. of peptone. An alkaline medium is preferable.
The flask was thoroughly sterilised before use, and is now plugged with
sterile cotton-wool and incubated at 77° C. for three or four weeks.
Pure air may be passed over the culture periodically, thereby aiding
the growth. After the lapse of about a month a scum of diphtheria
growth will have appeared over the surface of the fluid. This is now
filtered into sterilised flasks, and some favourable antiseptic added
to ensure that nothing foreign to the toxin shall flourish, and the
flasks are kept in the dark. Here, then, we have the product, the
toxin, ready for injection into the horse.
[Illustration: Flask used for the Preparation of the Toxin of
Diphtheria]
2. _Immunisation of the Horse._ It is evident that only healthy horses
are of service in providing healthy antitoxin, even as healthy children
are necessary in arm-to-arm vaccination. To provide against any
serious taint the horse is tested for glanders (with mallein) and for
tuberculosis (with tuberculin). The dose of the injection of toxin is
at the commencement about 1/10 cc., or a little more. The site of the
inoculation is the apex of the shoulder, which has been antiseptically
cleaned. A mere prick is the whole operation. After the first injection
there is generally a definite febrile reaction and a slight local
swelling. From 1/10 or 1/2 cc. the dose is steadily increased, until
at the end of two or three months[86] perhaps as much as 300 cc. (or
even half a litre) may be injected without causing the reaction which
the initial injection of 1/10 cc. caused at the outset. This shows an
acquired tolerance of the tissues of the horse to the toxic material.
After injecting 500 cc. into the horse without bad effect, the animal
has a rest of four or five days.
3. _To Obtain the Antitoxin._ During this period of rest the
interaction between the living body cells of the animal and the toxins
results in the production in the blood of an antitoxin. By means of a
small sterilised cannula, five, or eight, or even ten litres of blood
are drawn from the jugular vein of the horse into sterilised flasks or
jars. The top of the jar is closed by two paper coverings before it is
sterilised. Then it is again covered with a further loose one. Before
use the loose one is removed and replaced by a metal (zinc) lid, which
has been separately sterilised. This metal lid contains an aperture
large enough for the tube which conveys the blood from the cannula to
pass through. The tube, therefore, passes through the metal lid and two
paper covers, which it was made to pierce. When enough blood has passed
into the vessel the tube is withdrawn, and the metal lid slightly
turned. Thus the contained blood is protected from the air.[87]
The jar containing the blood (which contains the antitoxin) is next
placed in a dark, cool cellar, where it stands for two or three days.
During this time the blood naturally coagulates, the corpuscles falling
as a dense clot to the bottom, and the faintly yellow serum rising
to the top. The serum, or _liquor sanguinis_, averages about 50 per
cent. of the total blood taken. Sometimes antiseptics are added with
a view to preservation. It is generally filtered before bottling for
therapeutic use, and sometimes examined bacteriologically as a test of
purity.
4. _The Use of Antitoxins._ The antitoxins are now ready for injection
into the patient who has contracted diphtheria, and in whose blood
toxins are in the ascendency and under which the individual may
succumb. They are injected in varying doses, as we have already
pointed out.[88] The general result is that mortality has been greatly
lessened, and that in fatal cases there has been a considerable
lengthening of the period of life. Moreover, the whole clinical course
of the disease has been greatly modified, and suffering lessened.[89]