THE NUTRITION OF THE HEART 165 



The practical question, in so far as resuscitation of the heartbeat is 

 concerned, is therefore, How can ive get the necessary fluid under pres- 

 sure into the 'beginning of the aorta? Even if we were to transfuse fluid 

 under considerable pressure into the aorta through the carotid artery, 

 it would mainly follow the large vessels leading away from the heart, 

 only a fraction of it reaching the beginning of the aorta. To compel the 

 fluid to pass towards the heart we must introduce some obstruction to 

 its passage peripherally. This can be done by the injection of a consid- 

 erable dose of epinephrine (adrenaline) in normal saline solution through 

 the needle of a hypodermic syringe inserted into the tubing leading 

 from the burette or pressure bottle to the caiinula in the carotid artery. 

 As the perfusion fluid is running in, the epinephrine injection is quickly 

 made, artificial respiration and cardiac massage being meanwhile prac- 

 ticed. In the majority of animals it will be found that complete res- 

 toration of the normal blood pressure can be effected by this method. 

 Indeed by performing the resuscitation under aseptic conditions, some 

 animals may be permanently resuscitated so far as the circulation is 

 concerned, although the nervous structures, even after a few minutes 

 of " death," never reacquire their normal condition. 



The epinephrine acts mainly by constricting the small arterioles and 

 thus directing the bloodflow towards the heart, but partly also by a direct 

 stimulating action on the cardiac muscle. It does not, however, con- 

 tract the coronary vessels; on the contrary, it is said to cause these 

 slightly to dilate. 



THE RELATIVE IMPORTANCE OF THE VARIOUS CONSTITUENTS 

 OF THE PERFUSION FLUID 



We can study the chemical conditions necessary for resuscitation 

 of the heartbeat by observing the beat of an artificially perfused heart 

 while solutions of different chemical composition are being perfused 

 through the coronary vessels. At the outset we are impressed with the 

 fact that for successful resuscitation the organic constituents of the 

 nutrient fluid are of trivial importance compared with the inorganic 

 constituents. With a solution containing the proper proportion of in- 

 organic salts, and of course an adequate supply of oxygen, the heart 

 of a rabbit, for example, may be made to continue beating for several 

 days. It is true that it will beat longer if some of the organic con- 

 stituents of the blood plasma, particularly carbohydrate, are present, 

 but on the inorganic constituents alone its ability to beat is truly 

 remarkable. 



