resistance of a newly-born guinea-pig should differ from that of an
adult one. But what is very remarkable is, that if an older guinea-pig
be inoculated with the blood of one a day old; if a third, still
older, be inoculated with the blood of the second; and so on; the
virulence of the microbe will be gradually reinforced--that is to
say, the usual habit of this parasite to develop itself in the body
of the animal will be restored. The process may be likened to that of
an animal or vegetable species, passing by successive stages and long
sojourns, from one region to another very distant one, subjected to
quite new conditions of climate, and gradually becoming acclimatised
to the last one. How great, then, must be the importance of the medium
of cultivation, with regard to the virulence of the microbes of
communicable diseases! Cultivating the microbe by passing it from one
guinea-pig to another, we soon arrive at a strength capable of killing
guinea-pigs of a week, a month, or several years old, until at last
the smallest drop of the blood of these guinea-pigs suffices to kill a
sheep; and from the sheep we may pass on to the ox.
The same is the case with the microbe of fowl cholera. When it has
ceased to have any effect upon fowls, its virulence can be restored by
inoculating small birds. Blackbirds, canaries, sparrows, all die, if
the virus has not been too much attenuated; and the effect is similar
on young chicks. Thus by several successive transitions from bird to
bird a virulence may be fostered capable of destroying full-grown fowls.
These facts suggested to Pasteur certain inductions which may be well
founded. Is not the attenuation of the virus by the influence of the
air one of the factors in the extinction of great epidemics? And
may not the reappearance of these scourges be accounted for by the
reinforcement of the virulence?
'The accounts which I have read,' Pasteur remarked some months ago,
'of the spontaneous appearance of the plague in Benghazi in 1856 and
in 1858 tend to prove that this outbreak could not be traced to any
original contagion. Let us suppose, guided by the facts now known
to us, that the plague, a malignant disease belonging to certain
countries, has germs of long duration. In all these countries its
attenuated virus must exist, ready to resume its active form whenever
the conditions of climate, of famine, of misery present themselves
afresh. The condition of long duration in the vitality of the germs of
evil is not even indispensable; for, if I may believe the doctors who
have visited these countries, in all places subject to the plague, and
in the intervals of the great outbreaks of the epidemic, cases may be
met with of people attacked with boils, not fatal, but resembling those
of the deadly plague. Is it not probable that these boils contain an
attenuated virus of the plague, and that the passage of this virus into
exhausted bodies, which abound only too freely in periods of famine,
may restore to it a greater virulence?
'The same may be the case with other maladies which appear suddenly,
like typhus in armies and in camps. Without doubt, the germs which are
the authors of these diseases are everywhere scattered around, but
attenuated; and in this state a man may carry them about him or in his
intestinal canal without great damage. They only become dangerous when,
by conditions of overcrowding, and perhaps of successive developments
on the surfaces of wounds, in bodies enfeebled by disease, their
virulence is reinforced.'
_ETIOLOGY OF SPLENIC FEVER._
M. Pasteur had triumphed over splenic fever with as much rigour as
precision. But he considered that he had still to make one further
investigation. He had established the effects of the pest; he had
discovered a preventive method with which to combat it: he now
wished to know the origin of the evil. Whence comes splenic fever?
Why is it endemic in certain departments of France, in certain parts
of Russia, Germany, Austria, Italy, Spain, and America? How is it
sustained? It was for a long time believed that splenic fever was born
spontaneously under the influence of various accidental causes. M.
Bouley has related, in his learned work on the 'Progress of Medicine
by Experimentation,' that in 1842 the Minister of Agriculture, M.
Cunin-Gridaine, at the request of the deputies of the departments that
were ravaged by the epidemic, entrusted to M. Delafond, a professor of
the school at Alfort, the task of investigating this malady, commonly
called the 'blood disease,' in the districts in which it was raging.
He was to search out its causes, and ascertain whether they did not
result from the system of cultivation prevalent in the country.
M. Delafond arrived in Beauce. One fact struck him--namely, that almost
all the animals attacked by the disease were young, fine, and vigorous:
those, in short, that gave the best promise. Viewing the richness of
the soil and the abundance and quality of the crops in conjunction with
this observation, Delafond at once elaborated a speculative theory.
'The blood disease,' said he, 'is nothing but an overfulness--an excess
of blood circulating in the vessels, and especially the predominance in
that liquid of red globules.'
Starting from this idea, his one object was, by means of logical
deduction, to trace everything to this fundamental error. He analysed
the soil, and demonstrated to what extent it was fitted to furnish
crops that were rich and abounding in nutritive properties. He analysed
the plants. He then complacently referred the richness of blood of
the Beauce sheep to the richness in nitrogenous principles of the
substances on which they were fed. He examined the lesions of the
diseased animals, and concluded that they were the consequence of the
blood containing too large a proportion of the organic elements, called
globules, fibrine, albumen, and too small a proportion of water.
'Reduce the proportion of nutritious elements,' he wrote as his
advice to the agriculturists, 'mix roots with all that is too rich in
nitrogenous principles, and you will reduce in proportion the losses
caused by the excess of the ultra-nutritious substances with which you
supersaturate your cattle.'
'Such is the very logical conclusion to which Delafond was led,'
adds M. Bouley, ridiculing these observations, based on a method of
reasoning, instead of on the experimental method. 'And as a fresh
proof of his theory he mentions the fact that the disease decreases
as you descend the country towards the Loire. On the right bank of
that river--in Sologne, for instance, which is a low, sandy, damp
district--blood disease is unknown. In the arrondissements of Gien and
Montargis and in parts of those of Orleans and Pithiviers it prevails
but little. There, Delafond imperturbably remarks, the soil is sandy
and the herbage not nearly so rich as in the Beauce plateau; and there
the blood disease is consequently less common.'
When we consider that such opinions could be written unchallenged only
forty years ago, that they could even borrow a scientific character
from the inspiration that gave them birth, we can see the progress that
has since been made, and can realise how great were the obscurity and
uncertainty which have been dispelled by the experimental method.
The presence of a parasite having been brought to public notice in
the blood of animals suffering from splenic fever, at the very time
when Pasteur had shaken the belief in spontaneous generation, people
grew accustomed to the idea that the stricken animals might have
contracted the germs of the malady from the outer world, without any
spontaneous birth, strictly so called, of the disease. This opinion
was strengthened by a knowledge of the spores of the splenic bacillus.
Pasteur, aided by Messieurs Chamberland and Roux, commenced experiments
with a view to solving this difficult etiological question. The first
experiments took place in the fields of a farm at the village of St.
Germain, near Chartres. Several groups of sheep were fed on lucern
grass which had been sprinkled with artificially-reared splenic fever
bacteria, or with their germs or spores. Although all the sheep of the
same group absorbed an immense number of the spores of the parasite,
many survived, even after being visibly affected. Those that died
showed all the symptoms of what is called spontaneous splenic fever.
The period of incubation lasted as long as eight or ten days, although,
in its latter stages, the disease exhibited those startling features
which have caused a belief that the incubating period is a very short
one--short, that is to say, for those conditions of contagion where the
parasite is not deposited in its pure state under the animal's skin.
But if prickly plants (notably the pointed ends of dried thistle
leaves, or beards of barley blades cut into little bits about a
centimeter in length) were added to this infected food, the mortality
increased to a striking extent. On examination after death, the
lesions of these animals were found to be similar to those observed in
sheep which were attacked by splenic fever in sheds, or which died of
the disease in the open fields.
From that time forward, the idea which had been predominant in the
minds of Pasteur and his fellow-workers during all their inquiries, was
materially strengthened. They were convinced that the animals which
died of blood disease in the department of Eure et Loire had been
infected by germs or spores of the splenic microbe contained in their
food; but the question remained, Whence came these germs?
From the moment when all belief in the spontaneous generation of the
parasite is rejected, attention is naturally drawn to the possible
consequences which may arise from burying in the earth animals which
have died of splenic fever. In the greater number of cases, when the
knacker's establishment is too far off and the dead animal is of little
value, a trench is dug on the spot, at a depth varying from half a
meter to a meter. If the animal dies in a field, it is buried where it
falls; if it dies in a shed the body is carried into a neighbouring
field. There it is buried, and putrefaction sets in; and since all the
splenic fever filaments of the blood are destroyed by putrefaction, it
was thought that no dissemination of the germs of splenic fever, after
the animal had been buried, could occur. Pasteur showed that this
opinion rested on a superficial observation. Even when the animal is
not cut up, blood spreads itself outside of the body in more or less
abundance. Is it not an habitual characteristic of the disease, that
at the time of death blood issues from the nostrils and the mouth, and
that the urine is often bloody? All around the corpse, therefore, the
earth is polluted with blood. Moreover it takes several days for the
splenic fever microbe to resolve itself into harmless granulations by
the action of gases, other than oxygen, which putrefaction generates.
During this time, the excessive inflation of the dead body causes
the liquids of the interior to issue from all the natural apertures.
How often also, a rent in the skin or the tissues increases this
flow. The blood and other matters, mixed with the surrounding aerated
soil, are no longer in the conditions of putrefaction, but rather in
those which form a suitable medium of cultivation for the microbe.
Experiments confirmed these views. Adding some splenic fever blood
to earth sprinkled with the water of yeast, or with urine, at summer
temperature, or at the temperature which the fermentation of a dead
body keeps up around it, as in a dung heap, in less than twenty-four
hours the splenic fever filaments deposited with the blood had
multiplied and resolved themselves into spores. These spores were
afterwards found in their state of latent life, ready to germinate and
to communicate splenic fever, after remaining in the earth for months,
and even years.
These experiments, curious as they were, were only, so to speak,
laboratory experiments. It was necessary to investigate what happened
in the open country with all the variations of dryness, of damp, and of
cultivation. A happy inspiration came to Pasteur and his assistants.
They had buried in the midst of summer, in an isolated corner of the
farm of St. Germain, near Chartres, a sheep which had died of natural
splenic fever, and of which they had made the autopsy. Ten months
afterwards, and again fourteen months afterwards, the idea occurred
to them of collecting some of the earth from this grave. After having
examined it, and established the presence of the spores of the microbe,
they produced, by the inoculation of guinea-pigs, the splenic disease
and death. But the circumstance which deserves the greatest attention,
is that the same experiment was successfully made with the earth on
the _surface_ of the grave, though this earth had not been disturbed
during the interval. Some experiments were afterwards made on the earth
of some trenches dug in a meadow of the Jura, where some cows which
had died of splenic fever had been buried at a depth of two meters.
Two years afterwards, by successive washings of the earth on the
surface of the graves, deposits were extracted which at once produced
splenic disease. At three trials within these two years the same
surface earths produced splenic fever, while, away from the graves,
the earth exhibited nothing of the kind. Finally, Pasteur and his
assistants proved that on the surface of the earth which covered the
buried animals, the germs were again found, after all the operations of
ploughing, sowing, and reaping.
But how, it will be asked, can the earth, which is so powerful a
filter, allow the germs of microscopic organisms to rise again to its
surface? Is one not tempted here to quote Pasteur against himself,
since, in his joint researches with M. Joubert, Pasteur had proved
that the waters of springs issuing from the earth, even at a shallow
depth, are entirely free from germs? Such waters, nevertheless, being
supplied from the earth's surface, which is constantly washed by rain,
the effect must be to carry down the finest particles to the springs.
But these latter, notwithstanding conditions so conducive to their
pollution, remain perfectly pure. Can there be a better proof that
earth of a certain thickness will arrest all solid particles, even the
most minute? Nevertheless, in these experiments on splenic fever, we
hear of microscopic germs, starting from the depths and coming up to
the surface--that is to say, in a direction contrary to the flow of the
rain. This is an enigma.
The explanation will cause surprise. The earth-worms transport the
germs, and bring up, from the depths where they lie buried, the
terrible microbes. In the tiny cylinders of earth which the worms
deposit on the surface of the soil, after the dews of the morning or
after rain, the splenic germs are to be found. It is easy to prove
this directly. If in earth, with which spores of the microbe have been
previously mingled, we place some worms, and at the end of several days
open the bodies of these worms, with all necessary precautions, so as
to extract from them the earthy matter which fills their intestinal
canals, we find in them large numbers of splenic fever spores. It
is, then, absolutely proved, that if splenic fever germs exist, as
they often do, in the light earth which covers the pits in which
animals dead of that disease lie buried, these germs result from the
disintegration by rain of the little excremental cylinders deposited by
the earth-worms. The dust of this disintegrated earth spreads itself
over the grasses on a level with the soil, and thus it is that animals
come to find on the pasture-field, and in particular kinds of forage,
the germs of splenic fever by which they are infected.
'In these results,' said Pasteur a short time ago at the Academy of
Medicine, 'what outlooks are opened to the mind in regard to the
possible influence of earths in the etiology of diseases, and the
possible danger of the earth of cemeteries!'
The earth-worms also bring to the surface other germs, which,
while they are as harmless to the worms as the splenic germs, are
nevertheless bearers of diseases to which animals are liable. All sorts
of germs are found in them, and the germs of splenic fever are in fact
always associated with those of putrefaction and septicæmia.
* * * * *
'And now,' concluded Pasteur, when laying before the Academy a rapid
survey of the etiology of splenic fever, 'is not the remedy naturally
indicated? We should never bury animals in fields destined either for
cultivation, for forage, or for sheep pasture. When it is possible a
sandy soil should be chosen for the purpose, or any poor calcareous
soil, dry, and easily desiccated--in a word, soil not suited to the
existence of earth-worms.' M. Tisserand, Director of Agriculture, has
remarked that splenic fever is unknown in the region of the Savarts
of Champagne, although it is surrounded by countries invaded by the
disease. If the conditions of commerce introduce splenic fever, it is
but a passing accident. Must not this be attributed to the fact that
in these poor soils, such as that of the camp at Châlons, where the
thickness of arable soil is only from 4 to 5 inches, superposed upon
chalk, the worms cannot live? In such a soil the burial of a splenic
fever animal will give rise to great quantities of germs, which, owing
to the absence of earth-worms, will abide in the depths of the soil
and remain harmless. Finally, it has been proved that the countries
subject to splenic fever have an argillaceous-calcareous soil, and that
the disease is unknown in schistose and granitic soils. The contrast of
the results, in relation to such differences of soil, is seen sometimes
in the Department of the Aveyron, between the right and left side of
one and the same road or watercourse.
May we not now in all confidence assert that, if the cultivators
choose, splenic fever may soon be a thing of the past among their
animals, their shepherds, and among the butchers and the tanners of
the towns, because splenic fever and malignant pustule are never
spontaneous? The disease exists only where it has been sown, or
where it has been diffused by the unconscious instrumentality of the
earth-worm.
The progress of vaccination will also contribute to the disappearance
of splenic fever; for this preventive, if extensively used, as there
is no doubt it will be, must end by establishing a race of domestic
animals which, having all sprung from vaccinated parents, will in
consequence be more resistant to the disease in its worst form. It
will be with them in relation to splenic fever as it is with ourselves
in relation to small-pox. It is a well-known fact that the ravages of
small-pox are much less considerable in our days than when it first
appeared in Europe. It is difficult not to attribute this, at least in
part, to the prevalence of vaccination.
In the populations where small-pox is introduced for the first time
it has an exceptional intensity. Some months ago a significant fact of
this nature occurred in Paris. A whole family of Esquimaux perished
from small-pox in the 'Jardin d'Acclimatation.' They had never been
vaccinated, nor had their ancestors. They were new to the attacks of
small-pox, which did not spread beyond them.
_METHOD OF DISCUSSION AND CONTRADICTIONS._
Every new discovery produces a revolution in general ideas; a
revolution gladly hailed by some, but opposed by others as disturbing
their habits of thought and reasoning. Those also who are thrown out
in their calculations, while engaged in working out a problem in any
way similar to the one that has been solved, too often atone for their
dilatoriness by furious denial of the newly asserted truth. The great
fact of the attenuation of virus, the artificial production of the
vaccines of chicken cholera and of splenic fever, the importance of
their employment for the preservation of animals from these diseases,
excited throughout the world a surprise and enthusiasm which passionate
critics soon sought to disparage. The fiercest attack was from Germany.
It commenced immediately after Pasteur's triumph at the International
Congress of Medicine held in London in 1881. The German doctor Koch
and his colleagues, MM. Gaffki and Lœffler, published in Berlin,
in the report of the German Sanitary Office, a kind of scientific
tirade against the discovery of virus vaccine, and the possibility of
utilising it in the large operations of cattle-breeding.
At the London Congress Dr. Koch had said to a French physician that the
possibility of attenuating virus was a thing too good to be true. The
whole question was therefore reopened by Dr. Koch and his disciples. At
first Pasteur let the torrent flow; but, not being the man to give way
before an adversary, he at last declared that the attacks of the German
savants must be repelled at Berlin itself. Continual applications for
splenic vaccine were made to him from different parts of Germany.
M. Pasteur replied that, seeing that the discovery was so formally
contested in Prussia, it would be well, before sending any vaccine
abroad, to institute a great demonstrative experiment, as had been done
at Pouilly-le-Fort.
Dr. Roloff, head of the Veterinary School of Berlin, hastened to
take the initiative, by an application to the German Minister of
Agriculture. The minister at once nominated a Commission to follow
the experiments in vaccination and to draw up a report for the German
Government. M. Pasteur entrusted the conduct of the vaccinations to his
new colleague, Louis Thuillier, who accepted with deep and silent joy
the management of an experiment that was to test a French discovery.
He was always ready for anything, this brave Thuillier, who was
destined to die, a martyr to the cause of science, in the full promise
of his youth, and in the full hope of glory. His courage and his work
were alike great and silent. In the laboratory he would spend days,
even weeks, without speaking, bent over his microscope with tenacious
resolution, endeavouring to follow Pasteur in all his investigations:
proud to live near his illustrious master, happy to be his disciple and
to be loved by him almost as a son. What a vacancy he has left in the
laboratory! What a place he might have held in science!
The composition of the German Commission, over which M. Beyer, member
of the Superior Council of Government, presided, showed clearly the
importance attached by Germany to the investigation of this French
discovery. Among its members was the famous Professor Virchow.
The experiments were carried out on the estate of Pakisch. The minutes
and reports of the Commission left no doubt as to the correctness of
the facts announced by Pasteur. But, as the negations of Dr. Koch and
his colleagues embraced questions beyond that of the prophylaxy of
splenic fever, Pasteur did not rest content with this initial success;
he sought for a fresh opportunity of convincing his opponents. This
opportunity occurred in September 1882, when an International Hygienic
Congress was held at Geneva. Thither went Pasteur, hoping to meet
Dr. Koch at the sittings; and he was not disappointed. Dr. Koch was
there, surrounded by his disciples. From the tribune of the Congress,
Pasteur refuted his criticism, exposed his errors, and challenged
him to a discussion in the presence of competent judges. There was
an instantaneous salvo of applause, and everyone awaited Dr. Koch's
reply. But he declined all debate, reserving his case for careful and
deliberate statement in the press.
It took three months for Dr. Koch to bring out a small pamphlet,
and these three months had borne their fruit. The discovery of the
attenuation of virus, which had been so vehemently attacked only a year
before in the report of the Sanitary Office, was now extolled by Dr.
Koch as a discovery of the first importance. Being, however, unwilling
absolutely to stultify himself, he continued the attack by denying its
efficacy in practical agriculture.
* * * * *