All bodily functions are more or less directly controlled by the nervous system, hence nervous troubles are interwoven with the diseases of all other organs. Disorder of the nerve centres or nerve trunks affects the most distant parts over which these preside, or to and from which they convey nervous impulse. In different cases we see this operating through the sensory or motor functions, through lack of coördination or of balance, through modification of the circulation, respiration, secretion, absorption, nutrition, metabolism, special sensation, intellection, emotion, etc. These manifestations are less evident or less diagnostic in the lower animal, because we cannot fully avail of the subjective symptoms. While the human patient can tell us his feelings and experience in their regular order and succession, we can only infer most of these in the animal, through dependent objective symptoms. In many cases we cannot even infer for lack of these dependent symptoms. The practitioner must carefully watch for and accurately observe all objective symptoms, and seek to rightly interpret them. Among other things he must note the nervous conformation, organization and susceptibility; the hereditary nervous characteristics as seen in breeds, temperament, habit, aptitude to learn, docility, instinct, intelligence, emotions and affections, and judge the case in the light of these. Similarly he must take into account the hereditary, racial and individual irritability, obstinacy, restiveness, vice, alertness, sluggishness, stupidity, moroseness, and diagnose accordingly. Congestion, anæmia, coma, paresis, paralysis, may result from the nervous disorder and offer valuable concurrent testimony to the same. Allowance must always be made for the _use_ to which the animal has been put, thus _sexuality_ tells strongly in the horse, bull, boar, or ram which has been used for breeding and has become relatively indocile and even dangerous; _food_ tells in the horse that “shows his corn”, and in the dog fed on flesh; the comparatively untrained English race horse is far less docile than the one inured to saddle or harness and the horse fresh from the range, though previously trained, is far less tractable than the one in steady work. The _sexual products_ are especially liable to modify the temper, hence the docility of the gelding, and castrated mare, and the undisturbed life and steady growth and fattening of castrated animals from cattle to capons. _The products of certain diseases_ and many _drugs_ derange the innervation and intellection. Of this we have examples in the hebetude of the victims of milk sickness and dourine, in the wild delirium of rabies, in the varied nervous disorders that attend on the use of narcotics, essential oils, alcohol, chloral, sulphonal, trional, strychnia, lead, phosphorus, arsenic, etc. GENERAL SYMPTOMATOLOGY AND DIAGNOSIS.