544 CIRCULATION OF BLOOD AND LYMPH. 



studied experimentally the effect upon the heart of stimulating 

 simultaneously the inhibitory and the accelerator nerves. The work 

 done upon this subject by Hunt seems to make it very certain that 

 in all such cases the result, so far as the rate is concerned, is the 

 algebraic sum of the effects of the separate stimulations of the nerve. 

 The inhibitory and the accelerator fibers must be considered, 

 therefore, as true antagonists, acting in opposite ways upon the 

 same part of the heart. The existence of the accelerator nerves 

 makes possible, of course, their reflex stimulation. Experimentally 

 it is found that stimulation of various sensory nerves those of the 

 limbs or trunk, for instance may cause reflexly either an increase 

 or decrease in the heart rate, and as a matter of experience we know 

 that our heart rate may be increased by various changes, particu- 

 larly by emotional states. The natural explanation of such ac- 

 celerations is that they are due to reflex stimulation of the nerve 

 cells in the central nervous system which give rise to the accelerator 

 fibers. But another point of view is possible. An increase in heart 

 rate may be brought about either by a reflex stimulation of the 

 accelerator fibers or by a reflex inhibition of the cardio-inhibitory 

 center. Hunt especially has presented many experimental facts 



Fig. 225. To show the acceleration and augmentation produced by a strong stimulus. 

 Isolated cat's heart, stimulation on left side. The upper curve gives the ventricular 

 contractions, the lower one the auricular contractions. The lowermost line gives the 

 time in seconds and the line above indicates the duration of the stimulation of the accel- 

 erator nerve. 



which indicate that an increase in heart rate from reflex action may 

 be produced by an inhibition of the tonic activity of the cardio- 

 inhibitory center. He finds, for instance, that when the two vagi 

 are cut stimulation of various sensory nerves fails to give any 

 increase in the already rapid heart rate, while, on the contrary, 

 when the two accelerator paths are cut a reflex increase in heart 

 rate may be obtained readily. Hering,* on the other hand, gives 

 experimental evidence to show that the acceleration of the heart 

 following upon muscular exercise does not occur when the accel- 

 erator nerves are cut, a fact which seems to show that these nerves 

 may be reflexly stimulated. We may conclude, therefore, that 

 the accelerator and the inhibitory fibers are working constantly 

 * Bering, " Centralblatt f. Physiol.," 1894, viii., 75. 



