54 



THE MECHANISM OF THE CIRCULATION. 



\:c 



The Centres of the Caediac Nerves and Cardiac Eeflexes. 



After placing one electrode within the nostril of a frog, and the 

 other on a cross-section of the spinal cord at the level of the fourth or 

 sixth vertebra, the astounding observation was made by the brothers 

 Weber that tetanic excitation caused standstill of the heart. This 

 experiment led to the discovery of the function of inhibition. By 

 further experiments the Webers localised the seat of the inhibitory 

 power to the spinal bulb, in the region which lies between the optic 

 lobes and the lower end of the calamus scriptorius. 1 By using the 

 prick of a needle as a method of excitation, Eckhard' 2 more minutely 

 localised the inhibitory centre in the frog to be between the cerebellum 

 and the tip of the calamus scriptorius. In rabbits, after dividing the 

 spinal cord immediately below the medulla oblongata, excitation of the 



fifth nerve reflexly slows the 

 heart. 3 By the needle method 

 of excitation, Laborde 4 localised 

 the vagus centre in the cat to a 

 point in the middle of the spinal 

 bulb lying in the lateral part 

 of the floor of the fourth ven- 

 tricle. At this spot there is 

 situated a mass of grey matter, 

 which forms the accessory nuclei 

 of the hypoglossal, spinal ac- 

 cessory, and glosso-pharyngeal 

 nerves. 



The vagal centre can not 

 only be excited by the stimula- 

 tion of afferent nerves, but it 

 can also be influenced by the 

 direct action of blood on the 

 centre, and from the cerebrum. 

 The frequency of the pulse can 



be altered by psychical and 

 Fig. 37. — Posterior view of medulla oblongata of .• i „ V,. T 



the cat, showing N.C, position of "vagus emotional conditions. In many 



centre ; semi-diagrammatic— Laborde. men the pulse may be slowed 



by directing the attention to 

 the contemplation of painful subjects. It is constantly accelerated in 

 emotional patients by mere physical examination on the part of a 

 physician. In the case of an individual counting his own pulse, the 

 frequency often becomes diminished. 



Tarchanoff observed a medical student who could alter his pulse rate 

 at will. 5 He found that men with this faculty had generally a remark- 

 able power over their muscles ; for example, they could bend the third 

 joint of a finger independently of the other joints, or contract the 

 platysma muscle. 



In conditions of hypnotism, the pulse rate has been observed to 



1 Ed. Weber, " Handworterbuch d. Physiol., : ' 1846 (2), Bd. ii. S. 45. 



2 Beitr. s. Anat. u. Physiol. (Eckhard), Giessen, 1878, Bd. viii. S. 187. 



3 Fraucois-Franck, "Trav. du labor, de Marey," 1876, Bd. ii. p. 255. 



4 Arch, dephysiol. norm, etpath., Paris, 1888, p. 397. 



5 Arch. f. d. ges. Physiol., Bonn, 1885, Bd. xxxv. S, 109. Cf, Pease, Boston Med. and 

 $, Joum., 1889, vol. cxx. p. 525, 



