THE CIRCULATION OF THE BLOOD AND LYMPH 155 



itself with even 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-aug- 

 mentor, 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 improbable that the effect of a stream of afferent im- 

 pulses reaching the cardiac centres by any given nerve is deter- 

 mined solely by anatomical relations. The intensity and the 



FIG. 66. 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 augmentation of the ventricular beat is seen. The notches in the ventricular 

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



nature of the stimulus seem also to have something to do with 

 the result. For when ordinary sensory nerves are weakly stimu- 

 lated, 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 inhibition of the heart 

 through the fibres of the trigeminus that confer common sensa- 

 tion on the mucous membrane of the nose, the mechanical ex- 

 citation of the sensory nerves of the pharynx and oesophagus 

 when water is slowly sipped causes acceleration.* The stimula- 

 tion of the nerves of special sense is followed sometimes by the 

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



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

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



