CIRCULATION. 



171 



Centrifugal inhibitory nerves have been found as an anomaly in the right 

 depressor nerve of a rabbit. 1 



Pawlow divides the inhibitory and augmentor nerves into four classes — 

 (1) nerves inhibiting the frequency of the beat, (2) nerves inhibiting the force of 

 the contraction, (3) nerves augmenting 

 frequency, and (4) nerves augmenting 

 force. The origin of this subdivision 

 of the two groups generally recog- 

 nized was the observation that, in cer- 

 tain stages of convallaria poisoning, the 

 excitation of the vagus iu the neck — all 

 the branches of the nerve except those 

 going to heart and lungs being cut — re- 

 duced the blood-pressure without alter- 

 ing the frequency of the beat. Further 

 researches showed that the stimulation 

 of branch 3 (Fig. 36) even in unpoi- 

 soned animals reduced the blood-pres- 

 sure independently of the variable al- 

 teration simultaneously produced in the 

 pulse-rate. Stimulation of branch 5 

 produced an acceleration of the heart- 

 beat without increase of blood-pressure. 

 Other branches brought about rise of 

 pressure without acceleration, and in- 

 creased discharge by the left ventricle without alteration in the pulse-rate. 



These results are supported further by Wooldridge's observation that exci- 

 tation of the peripheral ends of certain nerves on the posterior surface of the 

 ventricle raised the blood-pressure without modifying the frequency of contrac- 

 tion, and by Roy and Adami's demonstration that certain branches of the first 

 thoracic ganglion lessen the force of the cardiac contraction without influencing 

 its rhythm. But the matter is as yet far from certain. 



Fig. 36.— Schema of the centrifugal nerves of 

 the heart according to Pawlow : 1, vago-sympa- 

 thetic nerve; 2, upper inner branch; 3, strong 

 inner branch; 4, lower inner branch; 5, upper 

 and lower outer branches; 6, ganglion stellatum ; 

 7, annulus of Vieussens; 8, middle (inferior) cer- 

 vical ganglion; 9, recurrent laryngeal nerve. 



The Centripetal Nerves of the Heart. 



The Ventricular Nerves. — When the mammalian heart i- freed from 

 blood by Avashing 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 Don-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 augmentor nerves, 

 for the characteristic effects 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 tis>ne, 

 1 liering: Archiv fur die gesammte Physiologic 1894, Ivii. p, 78. 



