An American text-book of physiology . atomically those of the frog. The correspondenceis by no means complete, but it is so great as to make the facts discovered bya study of the nerves and muscles of the frog of the utmost importance to are driven to such sources of information because of the great difficulty ofkeeping the muscles of warm-blooded animals alive and in a normal conditionafter removal from the circulation. Irritability of Nerves.—The following preparation suffices to illustratethe more striking effects of irritants upon a nerve. A frog is rapidly killed,and then the sciati
An American text-book of physiology . atomically those of the frog. The correspondenceis by no means complete, but it is so great as to make the facts discovered bya study of the nerves and muscles of the frog of the utmost importance to are driven to such sources of information because of the great difficulty ofkeeping the muscles of warm-blooded animals alive and in a normal conditionafter removal from the circulation. Irritability of Nerves.—The following preparation suffices to illustratethe more striking effects of irritants upon a nerve. A frog is rapidly killed,and then the sciatic nerve is cut high up in the thigh and dissected out fromits groove, the branches going to the thigh-muscles being divided. The leg isthen cut through just above the knee. This gives a preparation consisting ofthe uninjured lower leg and foot, and the carefully prepared nerve supplyingthe muscles of these parts. The leg may be placed foot upward, and fastenedin this position by a clamp which grasps the bones at the knee, the clamp. 40 AN AMERICAN TEXT-BOOK OF PHYSIOLOOY. being supported by an upright (see Fig. 3). This preparation can i\\v\\ be subjected to a variety of tests, Mechanioal Irritation.—If the nerve be cut, pinched, suddenly stretched, or subjected to a blow, the muscles of the leg willcontract and the foot will be quickly moved. Chemical IiTitation.—If acid, alkalies, vari-ous salfc^, glycerin, or some other chenncal sub-stances be placed upon the nerve, the musclesof the leg begin to twitch irregularly, and asthe chemical enters more and more deeply intothe nerve the movements will become moreand more marked, until finally all the musclesare actively contracted and the foot is heldstraight up. Fig. for determining Thermal Irritation.—l^ a hot iron, or the the irritability of nerves. flame of a match, be applied to the nerve, acondition of activity will be developed in the rapidly heated nerve-fibres, andbe responded to by more or less vigor
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