326 THE NERVOUS REGULATION OF THE HEART 



accordance with the character of the afferent impulses received by it. 

 Two views are held regarding the nature of this control. In the pres- 

 ence of an accelerator and inhibitor mechanism, it is believed that the 

 caraiac musculature is constantly under the influence of two types of 

 impulses which are antagonistic to one another in so far as the first 

 tends to increase, and the second to decrease the contractions. Con- 

 sequently, the cardiac frequency must be regarded as the product of 

 the interaction between these two factors. The afferent impressions 

 received by the center shift the balance either in the direction of accel- 

 eration or inhibition. They accomplish this end by causing a greater 

 number of impulses of either the former or latter kind to be generated 

 and to be conducted to the heart. In accordance with the second 

 view, it is held that the activity of the heart can only be increased by 

 a depression of the inhibitor mechanism. 1 Thus, it is assumed that 

 the afferent impulses, on reaching the cardiac center, lessen the re- 

 straint under which the heart is constantly held, and thereby permit 

 the accelerator influences to gain full power. In the absence of defi- 

 nite facts, it is somewhat difficult to decide which of these two processes 

 is normally at work. It would seem, however, that the frequency of 

 the heart is regulated under normal conditions solely by the inhibitor 

 center, slight changes in the rate of contraction being effected by altera- 

 tions in the tonus of the latter. Greater variations as well as aug- 

 mentor effects, however, necessitate an active opposition to the in- 

 hibitor influences by the accelerator center. For this reason, the 

 latter may really be regarded as an aid to the former; its active 

 participation being required whenever especially marked results are 

 to be obtained. 



It has been stated above that almost all sensory nerves convey 

 afferent impulses to the cardiac center and hence, practically all recep- 

 tors are in communication with the cardiomotor mechanism. Chief 

 among these are the retina, the organ of Corti, the semicircular canals, 

 the olfactory cells, the taste-buds, as well as the cutaneous and visceral 

 end-organs for touch, pain, and temperature. The impressions de- 

 rived from these sources, become operative either directly after their 

 reception or some time later after they have been associated in their 

 respective intracerebral centers. In the latter case, the stored im- 

 pulses which serve as expressions of our psychic life or belong to the 

 group of the emotions, need not affect solely the activity of the heart, 

 but may also involve respiration, secretion, as well as the responsive- 

 ness of smooth and striated muscle-tissue. In general, it may be stated 

 that pleasurable experiences decrease and annoying impressions 

 increase the cardiac rate. It should also be noted that these afferent 

 impulses may give rise to effects which actually endanger the life of 

 the individual. As an example of this kind might be mentioned the 

 so-called "reflex cardiac death" which may result whenever the in- 

 hibitor center is excessively stimulated. It should also be mentioned 



1 Hunt, Am. Jour, of Physiol., ii, 1899, 395. 



