=Disease= is an injurious deviation from the normal function or structure. The morbid process resulting in disease is usually in the nature of a modification of the normal or physiological condition, so that it is often difficult to set the exact limits of health and disease. What is a purely physiological process under given conditions, would be distinctly pathological under others. The free kidney secretion of cold weather and the profuse perspiration of a hot season are both purely physiological and in the main balance each other. Each under its special environment fulfills an essential work in eliminating from the system toxic materials which would prove hurtful if retained, and thus each is not only physiological but beneficial. If, however, they occurred, not in this mutually compensatory manner, but simultaneously in this profusion, they might well be dreaded as morbid conditions. Again if either were to occur apart from its normal causative environment, if for example the polyuria appeared in hot weather and the perspiration in cold, the phenomenon might fairly be called pathological. In any case if the excessive secretion induced a lowering of the general tone of health the process would be essentially a morbid one. In pronouncing therefore upon a morbid process one must take fully into account the corresponding physiological process, the attendant conditions, and whether the result is injurious or otherwise. The same is true of structural changes. What under given conditions would be essentially a morbid structure, might under other conditions be a simple adaptation to an unwonted environment, and a means of protection from injuries that would otherwise accrue. Excessive growth of cuticular tissue in the epithelioma, wart or corn is injurious and essentially pathological, while the callus on the camel’s knee or the workman’s palm is purely protective and physiological. The local development of a mass of fatty tissue in the average man or beast is a disease, but the tendency to the uniform deposition of fat in the connective tissue of the improved breeds of meat producing animals, is the happy culmination of a long continued and skillful selection and regimen, without which the live stock industry of today would be a grievous failure. To constitute disease, therefore, modified function must be permanent, and not simply a compensating increase, decrease, or other change, and it must be in some way injurious to the animal economy. Similarly to constitute disease modified structure must be other than a simple protection or beneficial change, it must not be a simple evolution in the nature of accommodation to the environment but it must be a cause of injury to function or a distinct deformity.