Page:The American Cyclopædia (1879) Volume XVI.djvu/415

VIVISECTION 395 the first to make any great and conclusive dis- coveries 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 hlood 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 ob- struct 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 func- tions 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 diagno- sis, 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 deter- mine to the small fraction of a second their duration. Investigations of quite as impor- tant 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, as- similation, 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 modi- fied by the degree and nature of the nervous force, it becomes a matter of the greatest im- portance to ascertain the mode of communi- cation 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 opera- tions in which sometimes the brain, either en- tirely or in parts, has been removed, or sub- jected to the action of stimuli. The diseased condition of various parts of the nervous sys- tem which has been found in post-mortem examinations has had its relations to the con- comitant disordered conditions of the bodily organs explained, not only by such post-mor- tem revelations, but by observing the influence which certain produced conditions of the ner- vous 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 de- capitated frogs and other lower animals, in which the exposed nerves were subjected to galvanic and other stimuli. Some of the im- portant discoveries of Sir Charles Bell in re- gard to the motor and sensory nerves of the spi- nal cord were made by experiments of this kind ; but they lack the conclusiveness of experiments afterward made by Magendie upon living ani- mals, 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 ani- mal. The first experiments upon the sugar- forming power of the liver were made by Ber- nard, 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, some- times scarcely a trace being found if examined immediately afterward, it was contended by Pavy and others that the sugar was a post-mor- tem production. But the later experiments of Bernard upon living animals have, as above inti- mated, demonstrated the existence of a glyco- genic 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 choles- terine is a product of nerve action, its forma- tion 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 com- pared by Flint to that of urea by the kidneys, and he has named that condition of blood poi- soning which is the consequence of an abnor- mal accumulation of cholesterine in the vital fluid " cholesteramiia." (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 fistulse, 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, as- similation, and nutrition. Among other nu- merous instances of the solution of physiologi-