The sciences of medicine and surgery are built upon experience gained through animal experimentation. Almost all our knowledge of the role which bacteria play in the production of disease has been gained through studies on the lower animals. Protective serums could never have been discovered except by such procedure. Even now it is possible to diagnose some of the diseases most harmful to man only by the employment of rabbits or guinea pigs as test subjects, or for the production of blood having special properties for use in making laboratory tests.

The latest branch of medicine to develop is inspired by the prospect of preventing disease instead of the old ideal of curing the sick. This new field of preventive medicine owes much to animal experimentation. Natural vitality enables the tissues to resist the entrance of certain bacteria, and constitutes a most effective defence for the body against many agencies to which in an enfeebled condition it would succumb. Our knowledge of the profound effect which the diet may exert on the vigor of the body is almost entirely the product of observations of the effects of specially planned experiments on small animals.

The study of the science of nutrition as a branch of preventive medicine has not been sufficiently appreciated in the past. It is true that the carbohydrate content of the diet of the diabetic has for many years been regulated as a therapeutic measure. Food has been selected with a view to the relief of constipation. Liquid or soft diets have been provided for the sick in certain conditions. Anti-scorbutic foods have been provided for persons who were subjected to conditions which experience had shown were likely to induce scurvy. The avoidance of excessive food consumption has been recommended. A low protein diet, a purin-free diet, sour milk as a therapeutic agent, and other dietetic regulations have been resorted to as means of affording nourishment specially suited to peculiar conditions.