Bacteriology and Therapeutics - Scientific Results Traceable to Animal Experiment Pathology

PATHOLOGY, BACTERIOLOGY AND THERAPEUTICS - SCIENTIFIC RESULTS TRACEABLE TO ANIMAL EXPERIMENT.

As examples of knowledge obtained in this sphere by animal experiment the following instances may be named:— (1) Inflammation.—Everychange in the tissues during in flammation—the slowing of the blood stream in the capillary ves sels, the escape of the leucocytes through their walls into the surrounding tissues, the stagnation of the blood in the affected part—all these were observed in such transparent structures as the web or the mesentery of the frog, the bat's wing, or the tad pole's tail, irritated by a drop of acid, or a crystal of salt, or a scratch with a needle. It was in the course of observations of this kind that Wharton Jones observed the rhythmical contrac tion of veins, and Waller and Cohnheim observed the escape of the leucocytes, diapedesis, through the walls of the capillaries. From these simple experiments under the microscope arose all our present knowledge of the minute processes of inflammation. Later came the work of Metchnikoff and others, showing the importance of diapedesis in immunity.

(2) Suppuration

and Wound Infection.—Lister's work on antiseptics and its modern extension—asepsis—depend upon knowledge gained in investigations of bacterial diseases produced experimentally in animals under diverse conditions.

(3) Anthrax.—InFrance between 1882 and 1893 over 3,000,00o sheep and nearly 500,000 cattle were inoculated against this disease by the preventive method discovered by Pasteur. The average mortality, before vaccination, for the whole of France, was io% in sheep and 5% in cattle; with vaccination it fell to 0.94% in sheep and 0.34% in cattle. In rouget (swine measles) the effect of preventive inoculation was even more striking, the mortality falling from an average of 20% to one of I.45%• (Chamberland, Ann. de l'Inst. Pasteur, March (4) Tuberculosis.—To animal experiments is owed our knowl edge of the nature of tuberculosis prior to discovery of the spe cific bacillus, proof that B. tuberculosis is the causal organism, the importance of associated suppurative micro-organisms in de termining the type of the disease, and the use of tuberculin for detection of tuberculous cows.

(5) Diphtheria.—Proofthat B. diphtheriae is the causal or ganism, immunization of animals against the disease, introduction of treatment by diphtheria antitoxic serum, discovery of the Schick preventive method of inoculation.

(6) Tetanus.—Thebacterial nature of tetanus and the mode of action of tetanotoxin were discovered and an antitoxic serum was prepared which is of great value as a preventive agent in animals and man. In the laboratory curative effects can be obtained by administration of the serum which, so far, are not paralleled in the natural disease.

(7) Rabies

(hydrophobia).—ToPasteur's animal experi ments we owe the whole process of preventive inoculation with emulsions of brain and spinal cord of rabbits artificially infected with rabies.

(8) Cholera.—The"comma bacillus" was discovered in 1883 and ten years later preventive inoculation was first carried out on an extensive scale by Haffkine in India.

(9) Bubonic Plague.

B.pestis was discovered in 1894 and subsequently the entire history of the disease, its relation to the rat-flea, the variations in type to which it is liable and the methods of preventive inoculation and serum treatment were worked out.

(10) Typhoid and Paratyphoid Fevers.

Thebacteriology of these began in 188o when B. typhosus was discovered, B. paratyphosus C was found in Mesopotamia during the World War. Protective inoculation against typhoid carried out in 1896 by Almroth Wright and Semple quickly showed its value. In the British Army during the World War a typhoid vaccine alone was used at first, but later a mixed vaccine of B. typhosus, B. para typhosus A and B. paratyphosus B. The results were a trium phant success. To animal experiment must also be ascribed dis covery of agglutination as a means of diagnosis (Widal's reac tion).

(11) Malta or Mediterranean Fever.

Discoveryof the causal micro-organism, of an immunizing serum for treatment and tracing of the origin of the disease to the milk of infected goats by means of agglutination reactions.

(12) Epidemic Meningitis (cerebro-spinal).

Discovery of the meningococcus by inoculation experiments and separation of different types by agglutination methods. Introduction of serum treatment for the disease whereby its mortality has been reduced to about one-half.

(13) Malaria.—The bulk of our knowledge of this disease, including the life history of the malarial parasite and the elabora tion of preventive measures founded thereupon, was obtained by observations on man, but was led up to by the study of closely similar blood parasites occurring in birds.

(14) Yellow Fever.

Discoveryof a special mosquito (Steg omyia) which conveys the disease from man to man. Prepara tion of a specific anti-serum.

(15) Sleeping

Sickness.—Experiments on animals have proved that this disease is due to specific parasites carried by tse-tse flies from man to man. By measures taken to obviate this method of infection the incidence of the disease has been re duced.

(16) Infantile Paralysis.

Flexner of the Rockefeller Insti tute has proved, by experiments on animals, the infective nature of this disease and its transmissibility by inoculation.

(17) Myxoedema.—Evidencethat removal of the thyroid gland in animals produces the disease and that subsequent feed ing with thyroid gland or thyroid extract effects a cure.

(18) The Action of Drugs.

A long list has been more or less fully worked out, of which the following are the chief : Aconite, amyl nitrite and the nitrites in general, belladonna, mem bers of the barbitone series, calcium chloride, cocain, chloral, digitalis, ergot, insulin, morphia, salicylic acid, strophanthus, the chief diuretics and diaphoretics.

(19) Snake Venom.—Experiment has shown that animals can be immunized against many times the fatal dose of the venom of various poisonous snakes and that the serum of an animal im munized against one type of snake venom is effective against other types. Anti-venomous serum is now used in many parts of the world on man and domestic animals for snake bite. (See VIVISECTION.) (S. PA.; W. S. L.-B.)