RELATION OF RHYTHM TO NUTRITION 7 1 99 



the most highly rhythmic part of the muscular tissue of the heart, the sinus, 

 sets the rhythm for the entire heart. 



The function of the nervous system, by this view, is not to originate the 

 rhythm, but to regulate it, the detail of which 

 will be discussed below. 



Relation of Rhythm to Nutrition. The 

 whole heart, like the muscular parts of which 



it is composed, responds delicately to its con- -| 



dition of nutrition. In the frog and the turtle 

 hearts the muscular fibers are brought in inti- 

 mate contact with the blood contained within 

 its cavities. In the mammalian heart, on the 



other hand, a distinct system of vessels, the 



^H^iBi^^^SI "G ~"~ 

 coronary vessels and the vessels of Thebesius, 



supply blood to the organ. If the heart is |t: 



supplied with nutrient fluid similar to its 

 normal blood, and with proper aeration to 

 insure plenty of oxygen, it contracts with a 

 strong rhythm for many hours. This rhythm, -- 



however, responds quickly to changes in the 

 composition of the nutrient fluid. An abundant 

 supply of oxygen is absolutely necessary to the 

 maintenance of rhythm in the mammalian 

 heart, though the heart, especially a cold- 

 blooded heart, will contract for a time in an 

 atmosphere of hydrogen. No doubt the 

 organic constituents of blood are very essen- 

 tial to the prolonged maintenance of rhythm 

 in the heart, but the heart is not dependent on 

 these ingredients for its immediate reactions. 

 The inorganic salts seem to be peculiarly 

 closely related to the development and char- 

 acter of the cardiac rhythm, figures 172, 173, 

 and 174. Both the cold-blooded heart and 



the mammalian heart respond very quickly to u 



the influence of these salts. The details of 



^^^35BBSH88E^5^^B _n 



this influence have been discussed on page 193. mH ^ " 



It is somewhat surprising, however, that the 



highly organized mammalian heart will con- 



tract rhythmically for hours on purely inor- 



ganic nutrient fluid, provided only that the 



oxygen be supplied in sufficient quantity and 



under high enough tension. The isolated 



It 



8* 



