Experiments on Animals. Stephen Paget
the work of Professor Pawlow, of St. Petersburg. His success is largely due to his recognition of the importance of keeping his experimental animals under the most normal conditions possible, and of studying the different parts of the alimentary tract in animals which were not anæsthetised, but which were free from any pain or even discomfort, either of which conditions materially interferes with the activity of the digestive glands. He therefore established in dogs fistulæ in chosen portions of the alimentary canal, analogous to the fistula which accident rendered so valuable in the case of Alexis St. Martin. Not only has the knowledge thus gained enabled the physician to understand the sequel of events in disordered digestion, but the success of the operative measures undertaken by physiologists for the elucidation of their science has emboldened surgeons to attack disease in the most various parts of the alimentary canal.
"Renewed study of the secretion of pancreatic juice evoked by the passage of the acid digestive products from the stomach into the small intestine, which had been described by Pawlow, has resulted in the discovery of a new class of chemical agents, which act as special messengers from one part of the body to another, and exercise an important function in determining the action of all parts to one common end.
"Respiration.—The investigation of the chemical properties of the colouring matter of blood, and of its compound with carbon monoxide, has resulted, in the hands of Dr. Haldane, in the laying down of measures for the prevention of accidents from choke-damp or after-damp in mines. The same investigation has resulted in the discovery of a method of determining the total amount of blood circulating in the body of a living man. The application of this method has already added largely to our knowledge of the pathology of different forms of anæmia, as well as of the conditions obtaining in heart disease. Experiments by Hill and others on the physiological effects of compressed air have shown the precautions which should be observed in all diving operations. A proper appreciation of these results by diving-engineers would not only entirely obviate the cases of 'caisson disease,' but would enable diving to be carried on safely to a greater depth than has hitherto been attempted.
"It is impossible, however, to enumerate all the physiological gains of the last twenty or thirty years, or to point out their manifold applications in the cure and prevention of disease. The full control of the processes of disease, which is the goal of the physician and the surgeon, can only be attained through an accurate knowledge of the conditions governing the functions of the healthy body. The foundation of medicine and surgery is physiology: and it is only on living animals that the processes of life can be investigated."
PART II
EXPERIMENTS IN PATHOLOGY,
MATERIA MEDICA, AND
THERAPEUTICS
I
INFLAMMATION, SUPPURATION, AND
BLOOD-POISONING
Pathology, the study of the causes and products of diseases, is a younger science than physiology: the use of the microscope was the beginning of pathology; and the microscope, even so late as sixty years ago, was very different to the microscope now. The great pathologists of that time had not the lenses, microtomes, and reagents that are now in daily employment; they knew nothing of the present methods of section-cutting and differential staining. But the publication in 1839 of Schwann's cell-theory marks the rise of modern pathology. In 1843, Darwin wrote his first draft of the doctrine of the origin of species; and Pasteur, that year, was in for his examination at the École Normale. The work of Schwann, Virchow, and Pasteur had such profound influences on science that the span of sixty years seems to cover the modern development of pathology: and this span of years is marked, half-way, by the rise of bacteriology. In 1875, when the Royal Commission on Experiments on Animals was held in London, the evidence was concerned practically with physiology alone: very little was said about pathology, and of bacteriology hardly a word. The witnesses say that they "believe they are beginning to get an idea" of the true nature of tubercle: and the evidence as to the nature of anthrax, given by Sir John Simon, reads now like a very old prophecy:—
"We are going through a progressive work that has many stages, and are now getting more precise knowledge of the contagium. By these experiments on sheep it has been made quite clear that the contagium of sheep-pox is something of which the habits can be studied: as the habits of a fern or a moss can be studied: and we look forward to opportunities of thus studying the contagium outside the body which it infects. This is not a thing to be done in a day, or perhaps in ten years, but must extend over a long period of time. Dr. Klein's present paper represents one very important stage of a vast special study. He gives the identification of the contagium as something which he has studied to the end in the infected body, and which can now in a future stage be studied outside the body."
Thirty years ago, there was no bacteriology, in the present sense of the word: and now the "habits" of these "contagia" have been studied, outside and inside the body, with amazing accuracy. It has been proved, past all possibility of doubt, that the pathogenic bacteria are the cause of infective diseases; they have fulfilled Koch's postulates—that they should be found in the diseased tissues, be cultivated outside the body, reproduce the same disease in animals, and be found again in the tissues of those animals. By an immeasurable amount of hard work crowded into a few years, this New World of bacteriology has been subdued. The Royal Commissioners of 1875, speaking of physiological experiments only, said, "It would require a voluminous treatise to exhibit in a consecutive statement the benefits that medicine and surgery have derived from these discoveries." If physiology in 1875 required a treatise, bacteriology in 1906 requires a library: and it is impossible here to give more than the faintest outline of some of the work that has been done.
But all pathology is not bacteriology; and it would take a treatise of prodigious length to set forth the work of modern pathology in the years before anything was known of bacteria. The microscopic structure of tumours and of all forms of malignant disease, the nature of amyloid, fatty, and other degenerative changes, and the chief facts of general pathology—hypertrophy and atrophy, necrosis, gangrene, embolism, and many more—all these subjects were studied to good purpose, before bacteriology. Above all, men were occupied in the study of inflammation under the microscope. It was this use of the microscope that revolutionised pathology; especially, it made visible the whole process of inflammation, the most minute changes in the affected tissues, the slowing and arrest of the blood in the capillaries, the choking-up of the stream, and the escape of blood-cells out of the capillaries into the tissues. Everything had been made ready for the fuller interpretation that was coming from bacteriology: the old naked-eye descriptions of inflammation were left behind; men set aside the definition of Celsus, that it was rubor et tumor cum colore et dolore—words that sound like Molière's jest about the vis dormitiva of opium—they watched inflammation under the microscope, in such transparent structures as the frog's web and mesentery, the bat's wing, and the tadpole's tail. It was thus that Wharton Jones discovered the rhythmical contraction of the veins in the bat's wing. The discovery of the escape of the white blood-cells, diapedesis, through the walls of the capillaries, was made by Waller and Cohnheim. To those who are opposed to all experiments on animals, it may seem a very small thing that a blood-cell should be on one side or the other of a microscopic film in a tadpole's tail; but this diapedesis, the first move of the blood in its fight against disease, is now seen, in the light of Metschnikoff's work, as a fact of very great importance.
The history of this transitional period, from the study of inflammation in transparent living tissues to the use, in surgery, of the facts of bacteriology, is told in Lord Lister's Huxley Lecture, October 1900. He describes how the foundations were laid in surgical pathology, by microscopical and experimental work on inflammation, coagulation, suppuration, and pyæmia, for bacteriology to build on: how his own share of the work began when he was house-surgeon to Sir John Erichsen at University College Hospital, and afterward to Mr. Syme