File:A text-book of physiology - for medical students and physicians (1916) (14767962434).jpg

Identifier: textbookofphysio1916howe (find matches)
Title: A text-book of physiology : for medical students and physicians
Year: 1916 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Medicine
Publisher: Philadelphia and London : W. B. Saunders Company
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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not only prevents the usualsystole, but also removes the to-nicity of the musculature. Exam-ination of the heart shows also thatthe inhibition affects the wholeheart,—both auricles and ventriclesare slowed or stopped, as the casemay be. That the vagus nerve inman also contains inhibitory fibersto the heart is made highly probableby everything known concerningthe conditions under which the heartis slowed or stopped temporarily,and has, moreover, been demon-strated directly in several instancesupon living men.* These inhibitoryfibers have been shown to exist inall classes of vertebrates and in anumber of the invertebrates,—afact which in itself would indicatethe great importance of their in-fluence upon the effective activity ofthe heart. In the mammals gener-ally employed in laboratory experi-ments the inhibitory fibers occur inboth vagi; in some of the lower vertebrates, however, especially inthe terrapin, the inhibitory fibers may be found exclusively ormainly in the right vagus.
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Fig. 239.—To show the inhibitionof the terrapins heart due to stimula-tion of the vagus nerve. The uppertracing (/) records the contractions ofthe left auricle; the lower (//) the con-tractions of the ventricle. The vaguswas stimulated three times, eachchamber coming to a complete stop.On removing the stimulus it will benoted that the auricular contractionsincrease gradually to their normal,while the ventricular contractionsstart off at full strength. * See especially Thanhoffer, Centralblatt f. d. med. Wiss., 1875, whogives an account of an experiment in which the vagi were compressed in theneck, with a resulting stoppage of the heart and loss of consciousness. THE CARDIAC NERVES. 583 Analysis of the Action of the Inhibitory Fibers.—The prom-inent effect of the action of the inhibitory fibers is the slowing

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