Part 10

The use of the microscope, however, lent a fresh vigour to the believers in spontaneous generation; and, forced to relinquish the mouse and the insect, they still found satisfaction in germs. In the middle of the eighteenth century the doctrine was firmly upheld by an English priest, one Needham, whose experiments, in spite of the keen, and as we now know, unanswerable criticisms of the Abbé Spallanzani, were so convincing that he was early elected a Fellow of the Royal Society. From his time till late in the last century, the question of the spontaneous origin of microscopic life has from time to time troubled the mind of man. Pasteur, Tyndall, and others have at length laid that ghost. It would take too much space to discuss all the experiments made to solve this question. Pasteur’s work did not escape the liveliest criticism; and eventually, in order to settle the matter, he appealed to the Academy of Sciences to appoint a Commission to report on the experiments of himself and his opponents. It is needless to say that when the Committee met and inspected the experiments of Pasteur, and listened to the excuses of his critics, they pronounced absolutely in favour of Pasteur.

In 1862 Pasteur succeeded Senarmont as a member of the Academy of Sciences; and, it is interesting to note, he was presented by the mineralogical section. During this year he had interested himself in the manufacture of vinegar, which is extensively carried on in and around Orleans. He investigated the action of the _Mycoderma aceti_, the mould whose activity converts alcohol into acetic acid; and he taught the manufacturers the importance of pure cultures, showing them how, by a careful manipulation of the temperature, and by artificially sowing the fungus which effects the chemical change, the product they sought could be produced in a week or ten days, instead of requiring two or three months. This problem naturally led on to the acetous fermentation of wine, the cause of great loss to French wine exporters. Pasteur was able to demonstrate that the sourness of wine is caused by various foreign organisms, each of which causes a peculiar flavour to appear in the wine it attacks. The bouquet of wine is notoriously a delicate object, easily disturbed; and the question arose how to check the growth of the organisms without interfering with the bouquet. Pasteur solved it as he solved similar problems with regard to milk. He was able to show that after wine is properly oxygenated, if it be heated to a temperature of some 55° to 60° C. the acid-forming micro-organisms are destroyed, whilst the bouquet is unaffected. Perhaps one of Pasteur’s greatest triumphs was his success in demonstrating this to a representative assemblage of wine-tasters, notoriously a very opinionative class of people.

Pasteur’s researches on micro-organisms further had a profound influence on operative surgery. To the presence of bacteria is due many of the dangers which used to follow on operations. If precautions are taken to exclude the harmful germs much suffering and danger are avoided. It was about this date--namely, in the spring of 1865--that Dr. (now Lord) Lister, who nobly acknowledged the debt he owed to Pasteur, performed his first operations under antiseptic treatment at the Glasgow Infirmary. This date marks an epoch in the history of human suffering.

The chemist Dumas was about this time a member of the French Senate, and in 1865 was charged with the duty of reporting on the petition of some 3,500 ‘propriétaires des Départements séricicoles’ on an epidemic which had for some years been destroying the silkworms of Southern France. Dumas was a native of Alais, a town of the Département Gard, situated in the centre of the silkworm industry, where also the distinguished zoologist Quatrefages was born. Anything that affected Alais affected Dumas; and the epidemic was destroying the prosperity of his native town. The disease was indeed becoming serious. Already in 1849 the silkworms were sickening. The stage at which the symptoms appeared varied--sometimes the eggs were sterile; at other times the silkworms hatched out but to die. If they survived they became shiny; black spots showed themselves; the worms moved with difficulty, refused to eat, and perished; or, if they lived long enough to pupate, the pupa either perished or the moth emerged in an enfeebled state and promptly died.

Efforts had been made to improve the stock by importing eggs from Spain and Portugal, but the Peninsula was soon affected. Eggs were then fetched from Turkey, Greece, and the adjacent islands. These countries too becoming infected, the French cultivators sent further afield and brought eggs from Syria and the Caucasus. Even this resource failed them, and in 1864 every silk-producing country in the world was infected, with the solitary exception of Japan. The loss to commerce was prodigious. In a normal year the value of the cocoons produced in Southern France is, roughly speaking, about £4,000,000; in the years 1863 and 1864 it had fallen below £1,000,000.

When Dumas first asked Pasteur to investigate the disease which was ruining large tracts of the South of France, the latter not unnaturally hesitated. ‘Considérez, je vous prie, que je n’ai jamais touché un ver à soie. Si j’avais une partie de vos connaissances sur le sujet, je n’hésiterais pas,’ he wrote to his friend; but in spite of his hesitation, he left for Alais, and at once commenced a campaign which lasted during the summers of the next five years. Almost immediately on his arrival he detected in the sick silkworms the corpuscles of Cornalia and Filippi, which we now call the _Micrococcus ovatus_. These micrococci are comparatively large and very bright; they occur in the tissues and blood of the silkworm, and are found even in the eggs of the moth. They cause the disease known as Pébrine. The occurrence of the micrococci in the eggs was one of the most important new facts observed by Pasteur. It was the first recorded instance of a parasitic organism being conveyed from one generation to another by the egg; and, although recently the germ of the Texas fever (allied to the malarial organism) has been shown to pass from one brood to another through the egg of the tick which conveys it, it is satisfactory to record that the cases in which this occurs are restricted in number and comparatively rare. The ease with which _Micrococcus ovatus_ could be detected suggested a remedy. A child, when trained, can readily identify the organism. Healthy moths produce sound eggs and healthy larvæ; diseased moths produce diseased progeny. At the present day, throughout the silkworm districts of the South of France, as soon as the moth has deposited her eggs on the piece of linen provided for that purpose, she is pinned up with the cloth; and during the ensuing autumn and winter the women and children are occupied in microscopically examining the body of the moth, crushed in a little water, for traces of the micrococcus. Should any be found, the eggs on the corresponding piece of linen are at once destroyed. Pasteur also showed that the infected stock spread the disease by distributing the micrococci on the mulberry-leaves, whence they enter the silkworm by the mouth; and that the sick inoculate the healthy by crawling over them and piercing the skin with their pointed claws. He therefore emphasized the importance of segregating the sound caterpillars.

The above account conveys no impression of the difficulties under which Pasteur worked. His researches were not only new to himself but to the world. Processes which at the present day are carried out by every medical student had to be devised for the first time. He had to combat the criticism of scientific men, and to overcome the almost invincible ignorance of the agriculturist, an ignorance which at one time advocated the desperate remedy of asperging with absinthe the leaves of the mulberry on which the silkworms fed.

Perhaps Pasteur’s greatest difficulty was the fact that the silkworms did not suffer from Pébrine alone; and it was some time before he recognized that he had to deal, not with one disease, but with two. The second disease, known as the ‘Flacherie,’ is a disease of the digestive system caused by overcrowding and insanitary conditions in the silkworm nurseries. Like Pébrine, it is caused by a micrococcus, _Micrococcus bombycis_. It was whilst investigating this creature that Pasteur discovered that, although the germ itself cannot survive a lengthy period of desiccation, it does in certain circumstances form spores which can survive conditions fatal to the mature organism. This is the first case recorded of a pathogenic organism producing spores, the existence of which has explained so many problems in the spread of disease.

During the period from 1865 to 1870 Pasteur was by no means occupied solely by the silkworm epidemic. In many respects it was a sad epoch in his life. Only nine days after his first arrival at Alais he was summoned to Arbois to see his dying father, but arrived too late. In the autumn of the same year he lost his little daughter Camille, the second who had died. In 1868 he himself was prostrated by a stroke of paralysis, and, although he slowly recovered, it left traces for the remainder of his life.

Few distinguished men of science are left to pursue their investigations undisturbed; and Pasteur was no exception. He had much to do with promoting the publication of the works of Lavoisier, for whose researches he had the profoundest respect. He actively intervened in the elections of the Academy of Science, which appears to consume an infinity of time. He made some preliminary investigations into cholera, an outbreak of which towards the end of the year 1865 carried off 200 victims a day in Paris. He spent a week at Compiègne as the guest of Louis Napoleon, and in a series of _séances_ explained the methods and results of his labours. He wrote on the work of Claude Bernard; he drew up schemes for certain reforms in the University; he gave advice on the higher education of the country, and tried to stem the troubles of the École Normale. In fact, he drew lavishly upon his reserve of health and energy until the breakdown of 1868 was inevitable.

After a tedious recovery he recommenced his work. The success of his methods had been acknowledged by the Austrian Government, who conferred on him in 1868 the prize of 5,000 florins offered to anyone who should succeed in discovering the best means of dealing with Pébrine. The same year the University of Bonn conferred on him the honorary degree of Doctor of Medicine; and in 1869 he was elected a foreign member of the Royal Society. As was to be expected, detractors were not wanting: but these were silenced by the campaign undertaken in 1869 by Pasteur on foreign soil. The Master of the Imperial Household, Marshal Vaillant, who devoted his declining years to scientific experiments, had repeated in his apartments in the Tuileries the observations of Pasteur on the silkworm disease, and had verified the accuracy of his conclusions. He suggested to the Emperor that the Villa Vicentina, a property belonging to the Prince Imperial, should be placed at Pasteur’s disposal for further research. This villa, situated a few miles from Trieste, belonged at one time to the Princess Élise, one of the sisters of Napoleon I., who had lived quietly there after the fall of the First Empire. On her death it passed to her daughter, the Princess Baciocchi, and she in turn bequeathed it to the Prince Imperial. It had been a great centre of the silkworm industry; but for some years no cocoons had been produced, owing to the ravages of the disease.

By short stages, owing to his precarious health, Pasteur made his way to Illyria, taking with him some sound silk-moth eggs, and during the winter not only confirmed his previous researches, but re-established the industry on such a scale that in the following spring the sale of cocoons from this estate alone reached the figure of 26,940 francs. During this winter he dictated to his wife the classic book in which he recorded the results of his last five years’ work. Pasteur returned to Paris through Munich, where he had the pleasure of meeting Liebig, one of the most determined of his adversaries. Although he was unable to induce the German savant to discuss scientific affairs, he always dwelt with pleasure on the courtesy and cordiality with which he was received.

On his return the Emperor nominated him a Senator for life; but, before the gazette appeared in which the nomination would have been recorded, war was declared. From his birth Pasteur had been an ardent patriot, and during the progress of the war he suffered acutely. So much did he feel the reverses of his country, and what he regarded as the undue harshness of the victors, that he felt constrained to return the diploma of Doctor of Medicine which two years before he had accepted from the University of Bonn. He did so in a letter which contained some expressions of feeling with regard to the head of the invading army. These had better have been omitted, but were perhaps pardonable under the circumstances; they in no way excuse the terms of reply which Dr. Naumann, Dean of the Faculty of Medicine at Bonn, permitted himself to use--terms which would be discreditable in an ill-bred street _gamin_.

From 1871 to 1876, the year in which he published his ‘Études sur la Bière,’ Pasteur was again largely occupied with the study of fermentation. Part of his object was undoubtedly to place the French brewers on an equality with the German; and in this he certainly had a large measure of success. To one who knew Paris under the Second Empire and who revisits it under the Third Republic, one of the first changes observable in the life of the _café_ is the enormous consumption of ‘bocks.’ Pasteur’s work, however, went far beyond the establishment of a national industry. He started investigations which have changed brewing from an art into a science; and his most fitting memorial in this respect is the bust which decorates the hall of the Carlsberg Institution at Copenhagen, an institution devoted to the study of all problems of fermentation. In his ‘Études’ Pasteur laid great stress on the fact that every fermentation is brought about by micro-organisms, and he dwells at length on the marked influence which certain bacteria exercise on the nature of the fermentations, and on the character of the beer produced. He did not, however, see, what Hansen demonstrated in 1883, that many of the commonest diseases of beer are caused by certain species of yeast-cell differing specifically from those which cause its normal fermentation. Indeed, he paid but small attention to species, regarding it as waste of time, as it undoubtedly often is, to trouble about names and synonyms.

As Professor Jörgenson and Dr. J. R. Green have shown in two recently-published works, we have learnt much about brewing during the last five-and-twenty years. The nucleus of the yeast-cell has been made visible by appropriate staining; some thirty different species of yeast-cell have been described, and their properties as ferments have been investigated; Buchner, by grinding up the yeast-cells, has produced an extract, called zymase, capable of converting sugar into alcohol; the fact has been established that it is not so much bacteria as other fungi, allied and often congeneric with the yeast-cell, which produce disease in beer; still, allowing a full measure of credit to later workers, we may look back to Pasteur’s researches in the early seventies as establishing for the first time a scientific basis for brewing.

The same remarks are applicable to Pasteur’s work on the diseases due to specific organisms in the region of preventive medicine. We have built and are building a lordly edifice, but he drew the plan and even laid the foundations. More than two centuries ago Robert Boyle--‘the Father of Chemistry and Brother of the Earl of Cork’--had said that he who could solve the nature of fermentations would be without doubt more capable than others of explaining certain phenomena of disease. Towards the end of his ‘Études sur la Bière,’ Pasteur wrote: ‘The ætiology of contagious diseases is on the eve of having unexpected light shed upon it.’ He was already thinking of his investigations into the cause and prevention of contagious disease.

There is a certain malady known, when it attacks cattle and sheep, as ‘charbon’ or ‘sang de rate,’ and when it attacks man, as ‘woolsorter’s disease.’ The term ‘anthrax’ covers the disease in both beast and man; and anthrax is produced by a bacterium known as _Bacillus anthracis_, which had been recognized and was accused of causing the disease before Pasteur began to interest himself in such matters. It annually carried off 20 per cent. of the sheep in the agricultural district of La Beauce, and in Auvergne some 10 to 15 per cent. In certain localities the loss was greater, amounting at times to an annual death-rate of 50 per cent. The disease was by no means confined to France; it was spread over Europe. In the government of Novgorod it was responsible for over 56,000 deaths in three years. In Egypt it was regarded as the direct descendant of the plagues of Pharaoh. It ravaged the large sheep farms of the Argentine Republic.

The bacillus which causes this disease, and which at times by inhalation effects a lodgment in the bodies of those engaged in handling wool and hides, was already known when Pasteur took up the study of pathogenic germs. About the same time it was also attracting the attention of the young German physician Dr. Koch, who subsequently became a severe critic of some of Pasteur’s work; but in this article we are dealing with Pasteur, and limitations of space compel us to leave unnoticed the brilliant work of many investigators who have made the latter end of the nineteenth century one of the greatest epochs in medical history.

Pasteur and his assistants made many fascinating studies on the behaviour and life-history of the _Bacillus anthracis_. He found it very susceptible to slight variations of temperature. The few degrees by which the temperature of a bird’s blood exceeds that of a mammal were sufficient to prove fatal to the bacillus; but by an ingenious experiment he showed that if the temperature of a bird be artificially lowered it becomes susceptible to the disease, though it readily recovers if the artificial surroundings be removed. Pasteur further noted that the bacillus was not equally fatal in all animals, and that it changed its character when passed through the body of certain classes of animals. It was, however, not in studying the _Bacillus anthracis_ that he made the far-reaching discovery of the attenuated virus. This he first noted when at work on chicken cholera, a disease very fatal in poultry-yards; and he made the important discovery by one of those happy accidents which only occur to those who possess the genius for observation. During his numerous experiments he one day chanced to inoculate some fowls with a forgotten culture some weeks old. To his surprise the chickens, though made ill, did not succumb; in fact, they rapidly recovered. He immediately tried what the effect would be if these same fowls were inoculated with fresh cultures of a kind so powerful as to be undoubtedly fatal to a healthy bird which had never suffered from the disease. To his delight, the inoculated fowls resisted the poison, and proved, in fact, immune. This simple experiment is the basis of the world-wide prophylactic measures which are now being carried on against all forms of bacterial disease; and, although Pasteur’s explanation of the weakening of the virus--which he attributed to oxygenation--has been shown to be erroneous, he must still be regarded as the originator of methods for the production of immunity by means of artificially attenuated organisms.

If the virus of chicken-cholera can be attenuated, and when attenuated produces immunity from later attacks, the same is probably true of other germs which can be cultivated outside the body. Arguing in this fashion, Pasteur returned to his study of anthrax. Here he also succeeded, and in the spring of 1881 he demonstrated the value of his treatment. Out of a flock of fifty sheep one-half were inoculated, the other half were not; the whole flock was then infected with the disease. In less than a month the uninoculated were dead of ‘charbon,’ the inoculated were perfectly healthy. The telegram announcing the result to Pasteur, anxiously waiting in his laboratory at Paris, ended with the words ‘Succès épatant!’

So striking a demonstration naturally had a profound effect. It inspired confidence in the treatment. Since the date of this experiment some millions of sheep have been inoculated against anthrax, and several hundred thousand oxen; and it has been calculated that, within the succeeding twelve years, seven million francs were saved by this means alone to French agriculture. Perhaps the convincing nature of Pasteur’s work in this connexion is best shown by the fact that the insurance companies of France insist on inoculation before they will insure sheep and cattle.

We have left ourselves but little space to dwell on the work which occupied the greater part of the last twelve years of Pasteur’s life. Already, in the midst of his work on anthrax, he was thinking of rabies; and in 1881 he proved that it was conveyed through the saliva of the mad dog, and that it could be communicated to rabbits. Saliva, however, was not in every case to be depended on. In some cases it failed to convey the disease. Experiment showed that the poison was concentrated in the brain. To this day no one has succeeded in finding the organism--if it be an organism--which causes rabies. Hence it cannot be cultivated on gelatine in test-tubes, and no modified culture of bacteria can be produced, as is now done in the case of diphtheria and other diseases. Other means had to be devised. After countless experiments it became evident that, if the spinal cord of a hydrophobic rabbit be kept dry at a temperature of 25° C. for a couple of weeks, the strength of the virus has so far vanished that, if an emulsion of the cord be injected, it produces no rabies, but has only a slight vaccinating effect. If two days later an emulsion of a twelve-days-old spinal cord be injected, the vaccinating effect is stronger; but the body, already inured to slight doses of the poison, remains unaffected. Thus, by gradually increasing the strength of the dose, a virus may at length be injected which would infallibly produce rabies but for the previous inoculations. When an animal is bitten by a mad dog, the poison transmitted takes some time to develop--some weeks at least, and often many months. If now the artificially introduced virus ‘gets the start,’ so to speak, of the naturally introduced poison, by the time the latter is at its height the animal has become gradually immunified to the specific poison and suffers little harm. The arsenic-eaters of the Tyrol afford an analogous case. They consume amounts of arsenic which would infallibly produce peripheral neuritis in men unaccustomed to such a diet.