however, closely approximated by the remarkable record established,
according to the recent researches of Dr. Krause, by typhoid, anthrax,
tubercle, and some other bacteria of preserving unimpaired not only
their vitality but their virulence after having undergone for a period
of twenty hours a pressure of no less than that of 500 atmospheres.
When we reflect that a pressure of 500 atmospheres is equal to a
pressure of about 7,500 pounds to the square inch, and that the normal
pressure under which life is maintained upon this planet is
approximately that of fifteen pounds to the square inch, this
bacterial victory over physical conditions will be more readily
appreciated.
The more intimate becomes our knowledge of bacteria, the more must we
marvel at the equipment with which they have been provided for
enabling them to maintain themselves in the struggle for existence--a
struggle which is as severe and as remorseless in this lowly region as
it is in those domains the inhabitants of which have risen to far
loftier heights on the great ladder of life.
SOME POISONS AND THEIR PREVENTION
Little did the learned Dutchman Leeuwenhoek dream when, more than two
hundred years ago, he recorded, in his _Arcana Naturæ_, that he had
found "viva animalcula" in his saliva, that this, the first beginning
of bacteriology, would lead, a couple of centuries later, to the
inauguration of a new era in the treatment of disease, in which these
so-called animalcula, from being considered as curiosities, would come
to be regarded as powers for good and evil of the first importance.
Protective inoculation or serum therapy, of which the public have
lately heard so much in connection with diphtheria, is the direct
outcome of bacterial investigations which during the last two decades
have been pursued with such zeal in every part of the globe.
The vast domain of immunity, which until recently was an undiscovered
country, is now being bit by bit annexed, and in all directions
workers are engaged upon opening up new tracts, in overcoming
difficulties, in changing chaos into order.
The problems which surround immunity are of so complex and subtle a
character that their mastery is by no means either easy or rapid, and
many recondite researches appear at frequent intervals on this subject
in foreign and other scientific journals, rendering it a difficult
matter to keep pace with the new discoveries and the latest theories.
The interest in this country in toxins and anti-toxins not unnaturally
centres round that branch of the subject which deals with diphtheria,
this disease having of late years figured so prominently in our
mortality tables, whilst the production of diphtheria and other
anti-toxic serums has been so finely elaborated abroad that it already
constitutes an article of commerce, and doubtless helps to swell the
exports of our great continental commercial rival.
In this connection the following statistics, published by Dr. Jalzer,
of the Mülhaus Hospital, are of interest regarding the mortality from
diphtheria before and after the introduction and application of
diphtheria anti-toxin. The death-rate from this disease, writes Dr.
Jalzer, which in 1892 and 1893 was fully 50 per cent., fell in 1895 to
38·5 per cent., in 1896 to 28·8 per cent., in 1897 to 16 per cent., to
20 per cent. in 1898, 15·15 per cent. in 1899, and 18·75 per cent. in
1900.
So far the efforts which have been made to mitigate _human_ suffering
have attracted most attention; but it will be remembered that Pasteur,
before he commenced the study of hydrophobia, had already won his
laurels in combating disease in the victory he gained over anthrax,
the ravages of which so frequently decimated the herds of the French
farmer and robbed him of his well-earned return on his capital and
labour.
In summoning the brilliant Director of the German Imperial Board of
Health to South Africa to investigate the nature of rinderpest, and,
if possible, discover a means of protecting cattle from its onslaught,
the Cape Government afforded another opportunity for the scientific
study of a disease associated with animals, upon the successful
mastery and limitation of which the agricultural prosperity of South
Africa is so largely dependent, being as it is one of the most fatal
and contagious maladies to which cattle are subject. Apart from the
great commercial importance attending Dr. Koch's discovery of a device
whereby cattle can be immunised or protected from contracting
rinderpest when exposed to its contagion, this discovery is of great
scientific interest, inasmuch as it has inaugurated a new departure in
methods of immunisation.
The previous methods in vogue for inducing immunity in animals from a
particular disease consisted in converting the virus itself into a
vaccine, as was done by Pasteur in his classical investigations on
anthrax and its prevention; and secondly, the employment of anti-toxic
serums, in which the virus is not directly inoculated into the animal
to be protected, but in which an intermediary is employed between the
virus and its victim. This intermediary, or living machine for the
generation of the anti-toxin, is usually a horse, which is
artificially trained by being given gradually increasing doses of the
virus or toxin, until it ultimately withstands doses which in the
first instance would infallibly have killed it. When the animal has
arrived at this satisfactory stage or condition of complete immunity,
some of its blood is from time to time drawn off, and the serum thus
obtained constitutes the anti-toxin which now figures so prominently
in modern therapeutics. Besides diphtheria-anti-toxic serum there are
also those of tetanus, or lock-jaw, plague, the famous anti-venene
serum, about the discovery and preparation of which greater detail is
given later on, and many others which are still the subject of
experimental inquiry.
Now Koch's method for the compassing of rinderpest differed from both
the systems above mentioned, inasmuch as he neither employed
artificially weakened cultures of the virus, or an anti-toxic
rinderpest-serum; instead he took one of the natural secretions of an
animal infected with rinderpest, and by injecting this into a healthy
animal it was discovered that the latter, as is the case with a
vaccine, suffered only local and temporary discomfort, and acquired
pronounced immunity from the active virus. The secretion selected by
Dr. Koch and his assistant, Dr. Kolle, for this purpose was the gall,
and it might be supposed, from the fact that its inoculation into
healthy animals did not communicate the disease, that the rinderpest
bacteria were absent from the gall. But this is not so, for Dr. Kolle
has succeeded in isolating the latter from the gall of infected
animals, and, moreover, has proved them on isolation to possess their
full complement of virulence. Further investigations made by Koch and
Kolle have shown that the explanation of this seeming anomaly is to be
found in the fact that the gall of an animal suffering from rinderpest
contains a substance which prevents the migration of the rinderpest
bacteria, with which it is associated, from the point of inoculation.
Hampered in their movements by the controlling influence of this
special substance which has been generated in the gall, the bacteria
remain rooted to the spot where they are first situate, and only a
passing and exceedingly slight local affection results, which on its
departure leaves the animal with an immunity from rinderpest lasting
some four months. A number of interesting investigations have not
unnaturally been stimulated by this remarkable discovery, and
researches on the properties inherent in the gall of healthy animals
of various kinds have been recently carried out by Dr. Neufeld, of the
Institute for Infectious Diseases in Berlin, which are, however, of a
too technical nature to deal with here.
As an illustration of the practical use to which Koch's gall
immunisation method may be put in dealing with outbreaks of
rinderpest, reference to a recent report furnished by the Health
Officer of Shanghai may be of interest. Dr. Arthur Stanley describes
the outbreak as follows:--
"A large herd of cattle infected with cattle-plague was brought to
Shanghai from the Tanyang district, around the Grand Canal, for
export to the allied troops in the north of China. The disease
spread to an adjacent dairy, most of the cattle dying. On this
dairy becoming infected a police cordon was established round it
to prevent ingress and egress of cattle and ingress of persons
unconnected with the dairy, while the outside infected herd was
removed to an isolated part of the settlement. Having been
previously convinced of the futility of police cordons in the
prevention of cattle-plague, I was not surprised to find, within a
short time, that the disease had spread, by the meeting together
of cattle-coolies at a common tea-house, to three other dairies at
a distance of a quarter, a half, and two miles from the original
source of infection.
"As the animals are not, as a rule, taken away from the immediate
vicinity of the dairy, there being no grazing fields, and as
neither fodder nor dung is taken from one dairy to another, it is
practically certain the infection was carried by the
dairy-coolies.
"Immediately on this second series of dairies becoming infected it
was resolved to apply the gall immunisation method of Koch as
being the means at hand. About 1,500 cubic centimetres were
collected from the gall-bladder of a rinderpest animal, and 10
cubic centimetres were injected into the dewlap of each of the
twenty remaining cattle in the dairy.
"The injection caused slight local swelling and tenderness, but no
constitutional symptoms and no alteration in the milk-supply, an
important matter in a dairy. In all sixty-eight cattle were
injected with cattle-plague gall. Of these, seventeen were among
isolated uninfected herds; the remaining fifty-one belonged to
infected herds, and among the latter eleven died of cattle-plague
subsequent to the injection."
Dr. Stanley points out that ten of these animals, judging by the time
which elapsed _after_ the injection, when they showed the first
symptoms of the disease, _must have been already infected when the
injections were made_; the eleventh animal, however, undoubtedly
contracted the disease after and in spite of the injection.
"Considering," continues Dr. Stanley, "the usual excessive
mortality during an outbreak of this disease, the result may
almost be compared to the success of vaccination against
small-pox. Three young bullocks, each having received 20 cubic
centimetres of cattle-plague gall, were purposely exposed to
severe infection. They remained well, while unprotected animals
around them died of the disease."
In the domain of immunity there is, however, no more fascinating or
interesting story than that which deals with the discovery and
elaboration of a cure for snake-bites, a discovery which, while
attracting but comparatively little attention in this country, should
prove of paramount importance to our fellow-subjects in the great
Indian Empire. The significance to India of Professor Calmette's
discovery of a specific cure for snake-poison may be gathered, indeed,
from the statistics which have been compiled of the number of deaths
attributed by Indian officials to this cause alone, amounting, it is
said, to some 22,000 annually.
The Pasteur Institute in Paris has despatched many pioneers of science
to various quarters of the globe, but perhaps no scientific missionary
has produced more fruitful results than has Dr. Calmette. It was while
acting in the double official capacity of Médecin de 1st Classe du
Corps de Santé des Colonies and Director of the Bacteriological
Institute of Saïgon, in Cochin China, in the autumn of 1891, that
Calmette first commenced his experiments on the neutralisation of
serpent venom in the animal system.
He had, indeed, exceptional opportunities in the matter of serpent
venom wherewith to carry out his investigations, for during the rainy
season a village in the neighbourhood of Bac-Lieu (Cochin China) had
been attacked by a band of most venomous serpents.
These creatures, driven by the floods into the very huts of the
natives for shelter, created a terrible panic, and no fewer than forty
individuals were bitten by them. The panic was certainly not without
justification, for these serpents belonged to the species known as
_naja tripudians_, or _cobra de capello_, renowned for the deadly
nature of their venom, and widely distributed over India, Burmah,
Sumatra, Java, Malacca, and Cochin China; but until Calmette set to
work to systematically study the nature of this reptile's venom but
little precise or reliable information had been obtained as to its
character.
The governor of the district gave orders that as many as possible of
the reptiles were to be captured alive and forwarded to the Director
of the Bacteriological Institute, and a plucky Annanite actually
succeeded in securing ninety specimens, which were forwarded in a
barrel to Dr. Calmette.
This formidable gift was received with enthusiasm by the director, who
realised the importance and scope of the inquiry, which he at once set
himself to systematically work out.
Forty of these reptiles arrived alive, and several were at once
sacrificed to secure their venom glands. Each gland, resembling both
in size and shape a shelled almond, contains about thirty drops of
venom, and in this transparent limpid liquid is embodied a toxin of
extraordinary strength. It was, of course, necessary in the first
instance to ascertain, within as narrow a limit as possible, the exact
degree of toxic power inherent in the venom, and to determine, if
possible, the precise lethal dose in respect of each variety of animal
experimented upon.
A correct calculation of the quantity of venom required in every case
was, however, found to be quite impossible, for so virulent is the
poison that a single drop of an emulsion produced by pounding up eight
glands in 300 grammes of distilled water is sufficient, when
introduced into the vein of a rabbit's ear, to kill it in five
minutes. All the mammals to which Calmette administered this cobra
venom, such as monkeys, dogs, rabbits, guinea-pigs, rats, succumbed
more or less quickly, according to the size of the dose.
Small birds and pigeons die very rapidly, but the domestic fowl is
more fortunate, being somewhat less susceptible. Frogs also fall a
prey to the venom, but they are far more refractory than rabbits, for
it takes thirty hours to kill a frog with a dose of venom which would
infallibly destroy a rabbit in ten minutes. Toads, curiously, do not
enjoy to the same extent this power of resisting its toxic action, for
they die more quickly than frogs, whilst it makes short work of
lizards and chameleons. Fish form no exception to the rule, and even
invertebrates, such as leeches, are killed by minute traces of venom.
Whilst Calmette has found that the venom of different kinds of
reptiles exhibits marked differences in its toxic character, he has
also discovered that the venom secreted by one and the same serpent
varies considerably, according to the length of time the animal has
fasted. He describes how he kept a _naja haje_ (Cleopatra's asp) in
his laboratory, which during the whole eight months that it lived
never took any food whatever, although it was offered the most diverse
dainties. On its arrival it was made to bite on a watch-glass, this
being one method adopted for collecting the venom; the liquid was at
once dried, and 0·7 milligramme was found to kill a rabbit weighing
nearly four pounds in four hours. Two months later on, when the venom
was again collected, 0·25 milligramme proved a fatal dose. On the
death of the animal, at the end of eight months, the venom extracted
from the glands was so toxic that it only required 0·1 milligramme to
kill a rabbit of about the same weight as the previous one. The same
curious fact was noted in the case of a cobra's venom. Another
circumstance which appears to control the degree of toxicity inherent
in serpent venom is the interval of time which elapses between two
successive bites. The longer the interval the more virulent is the
venom; and Calmette points out that these observations are in
accordance with what has for a long time been known in France with
respect to indigenous vipers--that their bites are far more dangerous
and far more fatal in the spring, after the winter period of torpor is
over, than in the autumn.
Until quite recently it was thought that the only creatures which
could resist the fatal action of this poison were serpents, both
poisonous and non-poisonous. Calmette was led to this conclusion
because, although he inoculated large doses, as much as ten drops,
into cobras, they suffered absolutely no inconvenience, and the same
results were obtained with harmless snakes. On repeating these
experiments, however, and using much larger quantities of venom,
Calmette has found that they do ultimately succumb. That their
susceptibility in comparison with other animals is very slight, may be
gathered from the fact that a lethal dose of venom for reptiles is
roughly estimated to amount to as much as three times the quantity of
venom normally present in their respective poison glands. These
animals, therefore, although very refractory, are not absolutely
immune from the action of venom-toxin.
There are, however, other animals which enjoy a relative although not
absolute immunity to snake poison, and amongst these may be mentioned
swine, hedgehogs, and the mongoose. Swine, it is well known, will
greedily devour reptiles, and in some countries they are specially
trained up and employed for this purpose. Of particular interest,
however, are some experiments which were carried out to test the
traditional immunity towards this toxin ascribed to the mongoose.
These animals are very useful in sugar plantations, and are largely
employed to keep down the serpents and rats with which they abound,
for the carnivorous little mongoose is extremely partial to such prey.
Attempts have been made by sugar planters to introduce them into
Martinique, where they are not found in the wild state, as in the
island of Guadeloupe.
Six specimens of the mongoose were forwarded to Calmette from
Martinique, and these particular animals, it was stated, had never
been set at liberty since they were imported, so that they had had no
previous experience of snakes or venom. On arriving at the laboratory,
one of these little creatures was placed in a glass cage along with a
large cobra. The cobra, at once rising up and dilating its neck,
darted with fury upon the mongoose; but the latter, thanks to its
extraordinary agility, escaped being caught, and took refuge,
stupefied and terrified for the moment, in a corner of the cage. This
stunned condition, however, did not last long, for just as the
incensed cobra was preparing to make a fresh attack upon its
insignificant little victim, the latter, with wide-open mouth, rushed
and jumped upon the head of its enemy, viciously bit through its upper
jaw, and broke its skull in a few seconds. Thus, although in size but
a little larger than a squirrel, this tiny creature was more than a
match for a cobra two yards long.
Artificial inoculations of cobra venom into the mongoose fully
substantiated all the observed facts as to its remarkable immunity
from this poison. A dose sufficient to kill a large rabbit in three
hours was absolutely without effect; only when the venom was
introduced in quantities amounting to as much as eight milligrammes
was it followed by fatal results. Thanks, therefore, to their
extraordinary agility and remarkable power of resisting the effects of
this lethal toxin, these little animals are able to battle
successfully with the most dangerous reptiles.
The rapidity with which serpent venom becomes absorbed by the system
is almost incredible, and is well illustrated by the following
experiment. A rat was inoculated with venom near the tip of its tail.
_One minute later_ the latter was cut off a short distance above the
point of inoculation; but this operation was quite unable to save
the animal's life, for even in that brief interval the poison had
accomplished its fatal work, and a few hours later claimed its victim.
This rapid diffusion of the venom helps to explain the difficulty
which is experienced in arresting the course of the poison by local
treatment, for its passage is too rapid to permit of its being
overtaken by superficial measures of even the most stringent
character. But Calmette points out that local precautions are not to
be neglected, for although they cannot nullify the action of the
venom, they undoubtedly do delay its progress, and thus create a
longer interval or respite, during which an opportunity is afforded
for administering the anti-toxin. Before, however, passing on to the
investigations which have culminated in the production of a specific
antidote for this terrible toxin, there are a few more details which
Calmette has furnished as to its character which are of interest.
Serpent venom is characterised not only by its intensely virulent
properties, but also by the tenacity with which it retains them under
diverse circumstances. Thus it may be stored up for a whole year, and
yet at the end of that time be as active as ever; and even after
several years, although its toxic powers are somewhat reduced, it
still retains them to a very appreciable extent.
Unlike the bacterial toxins, this venom toxin can stand exposure to
considerable temperatures without injury to its activity, and that of
the cobra only suffers after it has been submitted to 98° Centigrade
for twenty minutes. Sensitiveness to temperature varies, however,
with the snake from which the venom is derived. Thus the venom of
the so-called "tiger-snake" of Australia will stand being exposed
for ten minutes to from 100° to 102° degrees Centigrade, and its
virulence only disappears when this temperature has been applied
for twenty minutes. The venom of the "black snake," another
Australian variety, loses its toxicity at a temperature of between
99° and 100° Centigrade; whilst an exposure to only 80° Centigrade
for ten minutes is sufficient in the case of viper venom, according
to Messrs. Phisalix and Bertrand, to profoundly modify its lethal
action. A continuous exposure for a fortnight to a temperature of
38° Centigrade does not affect cobra venom in the least; but if during
that same time it has been placed in the sunshine, it entirely loses
all its lethal properties. Thus, a pigeon was inoculated with about
thirty drops of venom which had been exposed to the sun's rays for
fourteen days, and it survived; whilst another pigeon was inoculated
with a little over six drops of similar venom which had been kept
during this time in the dark, and it died in a quarter of an hour.
All these elaborate researches as to the character of serpent venom
were essential to enable the next step to be taken in the elaboration
of the antidote. Before this great achievement could be accomplished
it was necessary to first succeed in artificially immunising animals
against the effects of this powerful toxin, so that the serum of such
animals could be applied for the protection and cure of other animals
from the effects of snakebites.