146 A MANUAL OF PHYSIOLOGY 



produced when they are excited mechanically by a rapid 

 succession of light strokes on the abdomen with the handle 

 of a scalpel (Goltz) . 



On the other hand, when the central end of an ordinary 

 peripheral nerve like the sciatic is excited, the common 

 effect is pure augmentation, which sometimes perhaps 

 develops itself with greater suddenness than when the 

 accelerator nerves are directly stimulated. Occasionally, 

 however, the augmentation is abruptly followed by a typical 

 vagus action. Here the reflex inhibitory effect seems to 

 break in upon and cut short the reflex augmentor effect. 



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 con- 

 nections 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 improbable that the 

 effect of a stream of afferent impulses reaching the cardiac 

 centres by any given nerve is determined solely by anato- 

 mical relations. The intensity and the nature of the 

 stimulus seems 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 reflex inhibi- 

 tion 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 some- 

 times 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. It is a remarkable fact, too, and one 



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

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



