462 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



OTHER CENTRIFUGAL HEART-NERVES. 



In the vago-sympathetic trunk and the annulus of Vieussens fibres pass to 

 the heart that cannot be classed either with the vagus or the augmentor nerves. 

 The evidence for their existence is furnished by Roy and Adami's observation 

 that when the intracardiac vagus mechanism is acting strongly, so that the 

 auricles are more or less completely arrested, the stimulation of the vago- 

 sympathetic trunk sometimes causes a decided increase in the force both of 

 the ventricles and the auricles, usually accompanied by an acceleration of the 

 rhythm of the heart. These changes are too rapidly produced to be aug- 

 mentor effects. 1 



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

 depressor nerve of a rabbit. 2 



Pawlow 3 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 in 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. 121) 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, 4 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. 6 But the matter is as yet far from certain. 



1 Koy and Adami, 1892, p. 249. 2 Bering, 1894, p. 78. 



8 Pawlow, 1887, p. 510. * Wooldridge, 1883, p. 537. 



5 Roy and Adami, 1892, p. 246. 



FIG. 121. Scheme 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. 



