CIRCULATION. 463 



THE CENTRIPETAL NERVES OF THE HEART. 



The Ventricular Nerves. When the mammalian heart is freed from 

 blood by washing it out with normal saline solution and the ventricle is painted 

 with pure carbolic acid, liquefied by warming, numerous nerves appear as 

 white threads on a brown background. They are non-medullated, form many 

 plexuses, and run beneath the pericardium obliquely downward from the base 

 to the apex of the ventricle. They may be traced to the cardiac plexus. 

 These fibres are not centrifugal branches of the vagus or the atigmentor nerves, 

 for the characteristic eifects of vagus and augmentor stimulation are seen after 

 section of the nerves in question. The stimulation of their peripheral ends, 

 moreover, the fibre being carefully dissected out from the subpericardial tissue, 

 cut across, and the cut end raised on a thread in the air, is without effect on 

 the blood-pressure and pulse-rate. The stimulation of the central stumps of 

 these nerves, on the contrary, is followed by changes both in the blood-pressure 

 and the pulse, showing that they carry impulses from the heart to the cardiac 

 centres in the central nervous system, or perhaps, according to the views of 

 some recent investigators, to peripheral ganglia, thus modifying the action of 

 the heart reflexly. 1 



Sensory Nerves of the Heart. The stimulation of intracardiac nerves 

 by the application of acids and other chemical agents to the surface of the 

 heart causes various reflex actions, such as movements of the limbs. The 

 afferent nerves in these reflexes are the vagi, for the reflex movements dis- 

 appear when the vagi are cut. 2 On the strength of these experiments the 

 vagus has been believed to carry sensory impressions from the heart to the 

 brain. Direct stimulation of the human heart, in cases in which a defect in 

 the chest-wall has made the organ accessible, give evidence of a dim and very 

 limited recognition of cardiac events for example, the compression of the 

 heart. 3 



Vagus. The stimulation of the central end of the cut vagus nerve, the 

 other vagus being intact, causes a slowing of the pulse-rate. The section of 

 the second vagus causes this retardation of the pulse to disappear, indicating 

 that the stimulation of the central end of the one affects the heart reflexly 

 through the agency of the other vagus. The blood-pressure is simultaneously 

 affected, being sometimes lowered and sometimes raised, the difference seeming 

 to depend largely on the varying composition of the vagus in different ani- 

 mals and in different individuals of the same species. 4 The stimulation of the 

 pulmonary branches, by gently forcing air into the lungs, loud speaking, singing, 

 etc., is said to increase the frequency of the heart-beat. 5 Yet the chemical 

 stimulation of the mucous membrane of the lungs is alleged to slow the pulse- 



1 Wooldridge, 1883, pp. 523, 529, 539 ; see also Lee, 1849, p. 43. 



1 Budge, 1846, p. 588; Goltz, 1863, p. 5; Gurboki, 1872, p. 289; Franck, 1880, p. 382. 



8 v. Ziemssen, 1882, p. 297 ; Nothnagel, 1891, p. 209. 



4 See Franck, 1880, p. 281 ; v. Bezold, 1863, p. 281 ; Dreschfeld, 1867, p. 326; Aubert and 

 Koever, 1868, p. 211 ; Kowalewsky and Adamiik, 1868, p. 546; Cybnlski and Wartanow, 1883; 

 Key and Aducco, 1887, p. 188; Arendt, 1890, p. 11 ; Roy and Adami, 1892, p. 251. 



6 Bering, 1871 ; Sommerbrodt, 1881, p. 602. 



