CARDIAC INHIBITION AND ACCELERATION 327 



that while the action of the heart cannot usually be influenced by 

 volition, certain cases are on record which clearly prove that a marked 

 voluntary control over this organ may be acquired at times quite inde- 

 pendently of emotional states or remote sensory impressions.^ 

 These volitional efforts most commonly produce an acceleration, but 

 may also induce a slowing of the heart. 



The frequency of the heart may also be lessened by exerting a slight 

 pressure upon the vagus at any point of its course along the neck.^ 

 As this procedure is not without danger, it should only be practised 

 with the greatest care. Augmentor or inhibitor effects frequently 

 result from tumors or serous effusions affecting either the medulla or 

 the cardiac nerves themselv^es. It should also be remembered that 

 the activity of the cardiac center is closely related to that of the 

 neighboring respiratory center, as is shown by the fact that the fre- 

 quency of the heart increases during inspiration.^ This reaction ap- 

 pears in the nature of a reflex which seems to have its origin in a central 

 stimulus rather than in one generated in the lungs themselves. Two 

 or three reasons may be given for this view. Thus, it has been found 

 that it persists during the spasmodic respiratory attempts following 

 the division of the cervical portion of the spinal cord,* and that it is not 

 in evidence in certain animals. This acceleration may be made more 

 striking by increasing the amplitude of the respiratory motions or by 

 heightening the general irritability of the central nervous system.^ 

 It has been suggested by Spalitta® that the stimuli upon which this 

 reflex depends, arise in the muscles normally employed in inspiration. 

 Deglutition possesses a similar influence, the cardiac acceleration be- 

 coming the more marked, the greaterthefrequency of these movements. 

 The opposite result may be produced by stimulating the mucous mem- 

 brane of the nasal cavity with the vapors of chloroform or other irri- 

 tants. This constitutes the so-called cardiac trigeminus reflex. 



An intimate functional connection also exists between the heart 

 and the systemic blood-vessels, because a higher arterial tension is 

 generally compensated for by a lessening of the activity of this organ, 

 while a low pressure gives rise to augmentor effects. Although the reflex 

 character of these changes cannot be questioned, some doubt exists 

 as to the precise locality in which these primary stimuli are produced. 

 Thus, it may be assumed that they arise in consequence of the varying 

 distention of the blood-vessels, but it is also possible that they are 

 generated in the heart itself, because this organ is equipped with sen- 

 sory corpuscles similar to those found in other structures.^ It is more 

 than probable that the high arterial pressure tends to stimulate these 



1 Tarchanoff, Pfluger's Archiv., xxxv, 1885, and van de Velde, ibid., Ixvi, 1897. 



2 Thanhoffer, Centralbl. fiir die med. Wissensch., 1875. 



3 First observed by C. Ludwig (Miiller's Archiv., 1847). 

 ^ Fredericq, Archiv de Biol., iii, 1882. 



^ Henderson, Am. Jour, of Physiol., xxxi, 1913, 399. 

 ^ Arch. ital. de Biol., xxxv, 1901. 

 ' Smirnow, Anat. Anzeiger, x, 1895. 



