Vivisection, (Lat. vivus, alive, and sectio, a cutting), a term used to designate cutting operations performed on living animals for the purpose of acquiring physiological and surgical knowledge, and sometimes also applied to operations in which cutting is not employed. The practice of vivisection dates back to very early periods, and was known in the Alexandrian school. Among the earlier operations which led to positive physiological knowledge may be cited those of Galen, who demonstrated the existence of blood in the arteries by passing two ligatures around an artery in the living animal; but he formed no conception of the manner of communication between the arteries and the veins, and believed that the septum between the ventricles of the heart was perforated by small orifices. Harvey was the first to make any great and conclusive discoveries as the results of experiments on living animals. In studying the movements of the heart, he exposed that organ in the inferior animals through a section made in the walls of the chest.

By experiments upon reptiles and fishes he showed that the heart receives its blood from the veins and discharges it into the arteries, a simple ligature to the large venous trunk being sufficient to cut off the supply, and one to the principal artery sufficient to obstruct the passage of the blood and to distend the heart. But although Harvey demonstrated the course of the circulation, it remained for Malpighi in 1661 to actually see the capillary circulation in the lungs of a living frog. It must be admitted that, however minutely the anatomy of the circulatory organs may have been studied upon the dead body, their functions could not have been determined without observing the action of the heart and arteries by exposing them to view in the living animal, and therefore the methods of physical diagnosis, such as auscultation and percussion, could not have been brought to their present state of precision. The question as to the relative time occupied by the auricular and ventricular contractions has only recently been determined by Marey, who constructed a very ingenious and delicate apparatus for registering the form and frequency of the pulse. (See Pulse.) By the use of his apparatus he was enabled to register at the same time the pulsations of the different divisions of the heart, and to determine to the small fraction of a second their duration. - Investigations of quite as important a character as those upon the circulation of the blood have been made for several years upon the various parts of the nervous system.

Since all of the vital processes of digestion, assimilation, and consequent nutrition, including also the circulation of the fluids of the body, depend chiefly upon nervous stimuli, and as the various forms of disease are greatly modified by the degree and nature of the nervous force, it becomes a matter of the greatest importance to ascertain the mode of communication which takes place between the different parts of the nervous system and the different organs of the body; and for this purpose the lower animals have been subjected to operations in which sometimes the brain, either entirely or in parts, has been removed, or subjected to the action of stimuli. The diseased condition of various parts of the nervous system which has been found in post-mortem examinations has had its relations to the concomitant disordered conditions of the bodily organs explained, not only by such post-mortem revelations, but by observing the influence which certain produced conditions of the nervous system of the inferior animals have upon the functions of their bodily organs.

Much knowledge in regard to the functions of the nervous system has been gained by means of experiments on executed criminals, and on decapitated frogs and other lower animals, in which the exposed nerves were subjected to galvanic and other stimuli. Some of the important discoveries of Sir Charles Bell in regard to the motor and sensory nerves of the spinal cord were made by experiments of this kind; but they lack the conclusiveness of experiments afterward made by Magendie upon living animals, in which the spinal canal was opened, and the cord with the roots of the nerves was exposed. - Vivisection has also afforded means of studying, with important practical results, the action of various forms of electricity on the animal body, and consequently of making an intelligent application of this agent in the treatment of disease. The relations of the production of sugar in the liver to the disease called diabetes mellitus have been determined by examinations of the blood obtained from the portal and hepatic veins in the living animal.

The first experiments upon the sugarforming power of the liver were made by Bernard, and at that time he used a decoction of the organ itself; but as the amount of sugar found in it seemed to depend upon the time after death of making the experiment, sometimes scarcely a trace being found if examined immediately afterward, it was contended by Pavy and others that the sugar was a post-mortem production. But the later experiments of Bernard upon living animals have, as above intimated, demonstrated the existence of a glycogenic function of the liver, by the discovery of sugar in the hepatic vein while there was none furnished to the liver. It has been satisfactorily established by Dr. Austin Flint, jr., by means of vivisections, that the liver, besides being a secretory organ, has also a special excretory function, viz., the elimination from the blood of cholesterine, a constituent of the bile. The same physiologist has also shown that cholesterine is a product of nerve action, its formation by the brain being indicated by comparing the proportion of cholesterine contained in the blood drawn from the carotid arteries of a dog and that contained in blood drawn from the jugular veins. (See " Text Book of Human Physiology," New York, 1876, p. 450.) The excretion of cholesterine by the liver is compared by Flint to that of urea by the kidneys, and he has named that condition of blood poisoning which is the consequence of an abnormal accumulation of cholesterine in the vital fluid "cholesterseniia." (See Cholesterine.) One of the most remarkable operations upon the living animal is the production of artificial diabetes by irritating the nervous substance in the floor of the fourth ventricle of the brain, which was first performed by Bernard. The production of intestinal fistula?, for the purpose of observing the action of the gastric juice and other digestive fluids upon various kinds of food, has led to the present advanced state of knowledge of the processes of digestion, assimilation, and nutrition.

Among other numerous instances of the solution of physiological problems are the discovery of the lacteals and their functions by Asellius in 1622; the practicability of the transfusion of blood by Lower in 1665, and the experiments afterward made upon the subject by Prévost and Dumas, Milne-Edwards, and others in the early part of the present century; also the investigation of the subject of rattlesnake wounds by Dr. S. Weir Mitchell in 1861, and their most appropriate treatment; and the explanation of the pathology and infection of the system by the tapeworm, cysticercus, and trichina spiralis, made by various observers between 1845 and 1860. - There has always been much discussion in regard to the practical importance of vivisection, and the involved questions of wantonness and cruelty, and considerable difference of opinion has existed. A report of the English royal commission (1876) gives a history of the subject, and considers the experiments on living animals under three principal heads, viz.: operations performed for original research or for demonstration to students; the administration of poisons and dangerous drugs, and operations connected therewith; and the artificial production of disease for the purpose of observing its progress and its cure.

The commissioners conclude that it is impossible, even if it were desirable, to prevent the practice of making experiments upon living animals, but they recommend the prohibition of its abuse by inhuman or unskilful persons, and of the infliction of unnecessary pain by all; and they furthermore advise the enactment of a law placing vivisection under the control of the secretary of state, giving him power to issue and revoke licenses, and binding the holders of them to conduct their experiments so as to produce as little suffering as possible consistent with the accomplishment of satisfactory results.