It was while still a youth, living with his master at Sudbury, that his mind first became deeply impressed on the subject of the cow-pox. A young country woman came to seek advice, when the subject of small-pox was incidentally mentioned in her presence, and she immediately observed, “I cannot take that disease, for I have had cow-pox.” This was a popular notion prevalent in the district, and not unknown to Jenner, but from this time he never ceased to think on the subject. On coming to London he mentioned it to several persons, and among others to Hunter; but all thought his notion of getting rid of small-pox Utopian, and gave him little or no encouragement. Hunter, however, who never liked to daunt the enthusiasm of inquirers, said, in his characteristic way: “Don't think, but try; be patient, be accurate.” About the year 1775, some time after his return to the country, he first had the opportunity of examining into the truth of the common traditions regarding cow-pox, but it was not until 1780, after much study and careful inquiry, that he was able to unravel the various obscurities and contradictions with which the subject was involved, and in that year he first disclosed his hopes and his fears to his friend, Edward Gardner. His mind seems to have caught a glimpse of the reputation awaiting him, and he felt that, in God's good providence, it “might be his lot to stand between the living and the dead, and that through him a great plague might be stayed.”
It would be impossible in the brief space at our disposal to recount the various difficulties and sources of error that Jenner encountered. It may, however, be mentioned that he ascertained that there was more than one form of local disease with which cows are afflicted, and which may give rise to sores on the hands of milkmaids, but that one only of these was the true cow-pox, giving origin to constitutional as well as local disease, and which proves protective against small-pox. He also found reason to believe that it was only in a particular stage of its development that the true cow-pox vesicle was capable of being transmitted so as to prove a prophylactic [preventive]. He was aware that though, as a rule, persons did not have small-pox a second time, yet there are instances where, from peculiarity of constitution or other causes, small-pox occurs a second time in the same individual. Such considerations as these cheered him to continue his inquiries when apparent exceptions occurred to the protective influence of true cow-pox.
Having at length satisfied his own mind, and, indeed, succeeded in convincing others also, respecting the important protective influence exerted on the constitutions of those who had received the true cow-pox in the casual way, he sought to prove whether it was possible to propagate the disease by inoculation from one human being to another. On the 19th May, 1796, an opportunity occurred of making the experiment. Matter was taken from the hand of Sarah Nelmes, who had been infected by her master's cows, and inserted into the arm of James Phipps, a healthy boy eight years of age. He went through the disease in a regular and perfectly satisfactory way. But was he secure against the contagion of small-pox? It is needless to say how full of anxiety Jenner was, when in July following he put this to the test by inoculating the boy with matter taken from the pustule of a small-pox patient. No disease followed! This, his first crucial experiment, Jenner related to his friend Gardner, and said: “I shall now pursue my experiments with redoubled ardour.” This ever-to-be-remembered day, 19th May, 1796, is commemorated by an annual festival in Berlin, where, in 1819, little more than twenty years after, it was officially reported that 307,596 persons had been vaccinated in the Prussian dominions alone. The account which Jenner has given of his own feelings at this time is deeply interesting. “While the vaccine discovery was progressing,” he says, “the joy I felt at the prospect before me of being the instrument destined to take away from the world one of its greatest calamities, blended with the fond hope of enjoying independence and domestic peace and happiness, was often so excessive that in pursuing my favourite subject among the meadows I have sometimes found myself in a kind of reverie. It is pleasant to me to recollect that these reflections always ended in devout acknowledgments to that Being from whom this and all other mercies flow.” Having obtained further corroboration of the truth of his conclusions by the vaccination of his own son and several others, he published in the form of a quarto pamphlet called “An Inquiry,” a brief and modest but complete account of his investigations and discoveries. By this the attention of the whole medical world and general public was called to the subject. His doctrines were put to the test and abundantly confirmed, so that Mr. Clive, the celebrated surgeon of the day, urged him to come to London, and promised him an income of £10,000 a year. Jenner, however, declined the request, saying, “Admitting as a certainty that I obtain both fortune and fame, what stock should I add to my fund of little happiness? And as for fame, what is it? A gilded butt forever pierced by the arrows of malignancy.”
Jenner always maintained that small-pox and cow-pox were modifications of the same disease, and that in employing vaccine lymph we only make use of means to impregnate the system with the disease in its mildest form, instead of propagating it in its virulent and contagious form, as is done when small-pox is inoculated. He felt, also, that there was this objection to the latter practice, which had obtained prevalence since its introduction to this country by Lady Mary Wortley Montagu, that the disease was thus spread among the community. He had, however, at that time to contend against the prevalent notions that epidemic diseases affecting the human race are peculiar to man and have no influence on the lower animals, and that the diseases of other animals are not communicable to man. But we have now abundant evidence that both these notions are erroneous. Jenner himself, indeed, had shown what was well known in various parts of the country, that the “grease” of the heel of the horse was frequently communicated to those who had the care of horses, whether or not it was the same disease as that which affected the cow. It is sufficient only further to adduce another disease of horses, called “farcy,” which is not infrequently fatal to grooms and others, not to mention the still more dreaded hydrophobia communicated by dogs and animals of the feline species.
The rapid acceptance and spread of Jenner's doctrines speedily silenced all cavillers except that small minority of incredulous and fanatical opponents who are always to be found refusing to accept any truth that does not coincide with their own ignorant and prejudiced views. The frightful mortality and appalling effects of small-pox prior to the introduction of vaccination were indeed such as to impel men to grasp at any means that held out a probability of escape from the scourge. In the present day the public can form but a faint idea of the ravages of small-pox before Jenner's time. The records of historians, not only of our own country, but throughout the world, teem with the most appalling accounts. Dr. Lettsom calculated that 210,000 fell victims to it annually in Europe. Bernouilli, an Italian, believed that not less than 15,000,000 of human victims were deprived of life by it every twenty-five years, i. e., 600,000 annually. In Russia 2,000,000 were cut off in one year. In Asia, Africa, and South America, whole cities and districts were depopulated. Nor was it only the actual mortality which rendered it so appalling. The records of the Institution for the Indigent Blind in our own country showed that three-fourths of the objects relieved had lost their sight by small-pox, while the number of persons with pitted and scarred faces and deformed features that were met with in the streets testified to the frightful ordeal that they had passed through. Multitudes died of diseases set up by this plague, or from ruined constitutions which it entailed. And what, of all this, it may be asked, do we now see? Is it not a rare thing to meet a person whose face is scarred and his features deformed by small-pox? How few persons can cite instances among their acquaintance of those who have died of small-pox after having been properly vaccinated? Is it necessary to go into statistics and elaborate investigations of the bills of mortality of the present day in order to be convinced that, as compared with the records of anti-vaccine times, we have indeed cause to bless the memory of Jenner?
We do not ignore the fact that small-pox, like other similar diseases having an epidemic character, may be absent for a length of time from certain districts and then break out again; nor that each epidemic has its period of increment and decrement, and varies in its degree of malignancy. But a full and careful review of the whole history of small-pox since the introduction of vaccination, proves to every unprejudiced mind that every recurring epidemic finds its victims, with comparatively few exceptions, among the unvaccinated, that its spread is arrested by renewed attention to vaccination and its vigorous enforcement, and that, even taking into account the countries and localities where from various causes it has been neglected, the mortality from this foul and fatal disease, small-pox, has been enormously reduced. Human lives have been saved, and human life prolonged to such an extent that it is impossible to estimate the benefits that mankind has derived from the genius and devoted patriotic labours of one man.
That doubts and difficulties in connection with this subject, involving the well-being of the whole human race, have lately arisen, must be admitted. But there is good reason to believe that, by modern researches on the subject of epidemic diseases and the germ theory of disease, these doubts are already being dispelled, and that the difficulties will be speedily obviated.
The grounds for this belief will be understood by the consideration of those scientific investigations to a brief detail of which we now proceed. The reader will then also be better able to judge of the propriety, and necessity of certain measures which, to the uninformed, must appear objectionable or even repulsive and arbitrary.
We now, then, turn to the remarkable experiments and discoveries of M. Pasteur, which have gained for him a world-wide reputation, and the bearing of which on the science of preventive medicine is commanding the attention and admiration of the whole scientific world, and indeed we may say of mankind at large. M. Pasteur is not a medical man, nor, indeed, a physiologist. He is simply a French chemist, a modest, retiring labourer in the field of science whose sole object has been the discovery of truth, and whose chemico-physical researches gained for him the Rumford Medal of the Royal Society in 1856. Having devoted himself specially to the chemistry of organic substances, he was naturally attracted by the discovery of Cagniard de la Tour, that yeast is really a plant, a species of fungus, whose vegetative action in fermentable liquids is the true cause of their fermentation. This was so opposed to the theories of all the chemists of the day, among whom may particularly be mentioned the celebrated Liebig, that it met with their warm opposition. When, however, Helmholtz and others succeeded in showing that by preventing the passage of the minute organisms constituting the yeast plant into fermentable liquids, no fermentation took place, the doctrine soon became established that the first step in the process of alcoholic fermentation is due, not to ordinary chemical changes, but to the presence of living organisms. In like manner the putrefaction and decomposition of various liquids containing organic matter was found to be due, not to the simple action of the oxygen of the atmosphere, but to the introduction from without of microscopic germs which found material for their development in such liquids. So that if by mechanical filtration of the air the entrance of such germs can be prevented, or if by heat or other means they can be destroyed, any fluid, however readily it may undergo putrefaction in ordinary circumstances, will remain perfectly sweet, though freely exposed to the air. And the same fluid will undergo a different kind of fermentation according as it is subjected to the action of different species of germs. These and other facts of scarcely less importance, which cannot here be detailed, induced Pasteur to test the application of the doctrines deduced from them to the study of disease in living animals.
His attention was first directed to the disease affecting the silkworm, and known as the Pebrine, which at one time seemed likely to destroy the silk cultivation both in France and Italy. It had been ascertained that the bodies of the silkworm, in all its stages of chrysalis, moth, and worm, were in this disease infested by minute corpuscles which even obtained entrance into the undeveloped eggs. After a prolonged and difficult inquiry, Pasteur found that these minute corpuscles were really independent, self-propagating organisms, introduced from without, and were not merely a sign of the disease, but its real cause. As a result of the application of these discoveries, the silkworm disease has been extinguished, or so controlled as to have saved a most important and valuable culture.