SYMPATHY (Gr. sympatheia, fellow-feeling) may be defined as the assumption by different individuals, or by different parts of the same individual, of the same or an analogous physiological or pathological state at the same time or in rapid succession. The late Dr. Todd (art. "sympathy" in the Cyclopedia f Anatomy and Physiology) divides all the examples of sympathy which are included in the above definition into three classes; first, sympathies between different individuals; secondly, those which affect the mind, and, through it, the body; and, thirdly, those which are strictly organic, and therefore physical.
As examples of the first class may be mentioned the readiness with which the act of yawning is induced in a company, if a single person begins to yawn; the facility with which hysterical convulsions are induced in a female hospital ward by a single•case; the fasci nation of its prey by the serpent, apparently by the power of the eyes; the similar power exerted by so-called electro-biologists and mesmerists, and by which some men can control even the fiercest carnivore. Of these sympathies the only explanation that can be given is that suggested in the article on Animal Magnetism (q.v.). As examples of the second class, the following cases may be adduced : certain odors—as of strawberries,. mutton, cats, and other most diverse objects—will induce fainting, in some people; the smell of a savory dish will excite a flow of saliva in the mouth of a hungry person; and the excitement of the emotions of pity will produce a copious flow of tears. In these
cases, an affection of the mind is a necessary link, but why that affection of the mind. should produce its peculiar effect, is a question -not easily answered; but it is plain that the portion of the nervous center which is affected in such cases, must have a direct influence upon the parts in which the sympathetic phenomena appear, through commis sural (or connecting) fibers, or the continuity of its gray matter with that of the center from which its nerves immediately spring. Examples of the third class occur in the pain in the knee which arises from disease of the hip-joint; the pain in the right shoulder from disease of the liver; the pain over the brow on taking a draught of iced water into the stomach; the various spasmodic affections connected with intestinal irritation, or the irritation of teething; the vomiting that occurs on the passage of a biliary or renal calculus, etc. All these cases may be more or less satisfactorily explained by the known laws of the sensory and motor nerves. In some of these cases the explanation, however, cannot be regarded as altogether complete. For example, the pain over the brow from the ingestion of cold water or ice into the stomach, may be referred to irritation of the gastric branches of the pneilmogastric nerves communicated in the medulla oblongata to the fifth nerve; but why the irritation should be confined to the frontal branch of first (or ophthalmic) division of the fifth nerve, we are utterly unable to explain.