328 THE NERVOUS REGULATION OF THE HEART 



end-organs by causing an overdistention of the ventricular cavities 

 or at least of the root of the aorta. This conception finds support in 

 the fact that even a moderate compression of the heart, as results 

 during the act of coughing or laughing, is usually associated with an 

 acceleration,' while the irritation of the endocardium most generally 

 gives rise to inhibitor effects.^ Less probable is the view that these 

 changes are occasioned by a direct action of the blood pressure upon 

 the constituents of the cardiac center. ^ 



One of the first proofs of the existence of these cardiovascular 

 reflexes has been furnished by Goltz^ who found that the frequency 

 of the heart may be reduced by simply tapping upon the surface of 

 the abdomen of a frog with a flat instrument. As this effect is not 

 obtained after the vagi nerves have been divided, there can be no ques- 

 tion regarding the reflex character of these impulses. On the afferent 

 side, their course may be either over the nerves of the cutaneous 

 sensations or over those relegating deep sensibilities from the viscera. 

 The latter contention seems the more probable. Very similar results 

 are obtained in mammals in consequence of the mechanical, thermal, 

 electrical or chemical stimulation of the abdominal viscera. Among 

 the large number of causes for this reflex may be mentioned the accumu- 

 lation of gas in the stomach or intestine,* inflammatory processes or 

 irritations of these organs by substances contained in the food, and 

 strokes upon the region of the solar ganglia. 



The cardiac acceleration commonly associated with increases in 

 the activity of the skeletal musculature, may be explained in different 

 ways. Thus, it may be held that the volitional impulses which are 

 generated in the cerebral hemispheres and are then conducted to the 

 muscles, overflow and affect the cardiac center directly. It may also 

 be assumed that the contractions of the muscles give rise to mechan- 

 ical impulses which influence the center reflexly. In the third place, 

 it has been thought possible that the activity of the center may be 

 varied by certain chemical substances formed in the course of muscular 

 exercise. This view finds confirmation in the fact that the function 

 of the center may be influenced either by varying the amounts of blood 

 supplied to it, or by altering the oxygen content of the circulating 

 blood. Thus, it has been found that the occlusion of the carotid and 

 vertebral arteries, as practised by Kussmaul and Tanner, is followed 

 invariably by a slowing of the heart. This reaction, however, does 

 not result if the vagi nerves have been divided beforehand. Very 

 similar effects may be obtained by lessening the oxygen content or 

 by increasing the carbon dioxid content of the blood. Even a slight 

 dyspneic condition suffices to augment the cardiac beats and rate, 

 while a more intense dyspnea invariably leads to partial and complete 



^ Pagano, Archiv ital. de Biol., xxxiii, 1900. 



2 Bie(ji and Reiner, Pfluger's Archiv, Ixxiii, 1898, 385. 



3 Virchow's Archiv fiir path. Anat., xxvi, 1863. 



* Burton-Opitz, Pfluger's Archiv, cxxxv, 1908, 205. 



