294 PHYSIOLOGY CHAP. 



oxygen under a pressure of two atmospheres. But the same effects 

 may be more simply obtained by the artificial circulation through 

 the coronary system of a physiological solution (to be described 

 below) saturated with oxygen, or even with air. It is essential in 

 both cases that the fluid should not stagnate in the vessels. 



Eusch (1898) found that the circulation of serum instead of 

 defibrinated blood necessitated a higher pressure to make it circu- 

 late with greater velocity, in order to provide the heart with the 

 quantum of oxygen necessary to its activity. 



Other researches on the necessity of oxygen to the survival of 

 the mammalian heart were instituted by Strecker (1900), and 

 more particularly by Magnus (1902), who was the first to circulate 

 gases instead of fluids through the coronary arteries of the isolated 

 cat's heart. He found, on injecting oxygen, that the heart beat 

 for about an hour. Its arrest is due to the permeability of the 

 vessel walls by gas. He saw that when hydrogen was injected in 

 place of oxygen, the heart continued to beat for about half an 

 hour, while it stopped after a few minutes when carbonic acid was 

 injected. The beneficent action of the circulating hydrogen 

 depends, therefore, upon the elimination of the carbonic acid 

 developed by the heart during its activity ; but hydrogen is not 

 sufficient to keep it going for a long time, and the heart ceases to 

 beat after it has exhausted all the oxygen which it holds in loose 

 combination. 



Winterstein controlled the importance of oxygen by circulating 

 Ringer's solution, charged sometimes with oxygen, sometimes with 

 nitrogen, through the coronaries of the isolated cat's and rabbit's 

 heart. He came to the following conclusions : 



(a) The mammalian heart requires external oxygen to main- 

 tain its activity. Its rhythm alters and it soon comes to a stand- 

 still, if nitrogen is substituted for oxygen. 



(&) If after a definite lapse of time the current of oxygen is 

 re-established, the heart is able to beat again. 



(c) It is possible to reproduce the state of asphyxia repeatedly 

 in the same heart, and in the above experiments it was observed 

 that the time necessary for reproducing asphyxial arrest was 

 shorter than that required for its first incidence. 



(d) The immediate condition of asphyxial arrest appears to 

 consist in the consumption of internal oxygen that takes place 

 during cardiac activity. 



Does the function of free oxygen, as the necessary condition of 

 the rhythmic activity of the heart, consist in the oxidation of the 

 muscular biogen which produces the alternate contractions and 

 expansions of the myocardium, or does it rather lie in the oxidation 

 of the toxic katabolic products that result from the metabolism of 

 the muscle, transforming them into innocuous substances, readily 

 eliminated ? 



