THE NERVOUS REGULATION OF THE HEART 



169 



These examples show that certain afferent nerves are especially 

 related to the cardio-inhibitory, and others to the cardio-augmentor, 

 centre, or at least that the central connections of some nerves are 

 such that inhibition is the usual effect of their reflex excitation, 

 while the opposite is the case with other nerves. But it is im- 

 probable that the effect of a stream of afferent impulses reaching 

 the cardiac centres by any given nerve is determined solely by 

 anatomical relations. The intensity and the nature of the stimulus 

 seem also to have something to do with the result. For when 

 ordinary sensory nerves are weakly stimulated, augmentation is 

 said to be more common than inhibition, and the opposite when 

 they are strongly stimulated. And while a chemical stimulus, like 

 the inhaled vapour of chloroform or ammonia, causes in the rabbit 



Fig. 78. Myocardiographic Tracing of Cat's Ventricle. The signal line shows the 

 point at which the central end of the brachial nerve was stimulated during 

 resuscitation of the animal after a period of cerebral anaemia. Some augmenta- 

 tion of the ventricular beat is seen. The notches in the ventricular tracing are 

 due to the artificial respiration. Time-trace, seconds. 



reflex inhibition of the heart through the fibres of the trigeminus 

 that confer common sensation on the mucous membrane of the nose, 

 the mechanical excitation of the sensory nerves of the pharynx 

 and oesophagus when water is slowly sipped causes acceleration.* 

 The stimulation of the nerves of special sense is followed sometimes 

 by the one effect and sometimes by the other. To complete the 

 catalogue of the nervous channels by which impulses may reach the 

 cardiac centres in the medulla, we may add that there must be an 

 extensive connection between them and the cerebral cortex, since 

 every passing emotion leaves its trace upon the curve of cardiac 

 action. The so-called ' reflex cardiac death,' which is an occasional 

 Consequence of intense psychical influences (anxiety, fright, etc.), 



* In 78 healthy students the average pulse-rate (in the sitting position} 

 was increased from 73 to 85 per minute by sipping water. 



