1G4 THE CIRCULATION OF THE BLOOD 



It is, however, obvious that in perfused preparations changes in pres- 

 sure are likely to cause alterations in rate as well as in force, unless 

 great care is taken to keep the heart itself as warm as the perfusion 

 fluid. 



The importance of an adequate pressure in the coronary vessels has 

 been clearly brought out in certain experiments in which the beat has 

 been maintained for a short time by establishing a pressure in the cor- 

 onary vessels by means of indifferent fluids or gases. Thus, if oxygen 

 gas is allowed to pass through the vessels under pressure, the heart will 

 beat for a short time, and the same result has been observed even when 

 mineral oil or mercury has been perfused under pressure (Sollmann). 



The necessity for an adequate oxygen supply is very readily demon- 

 strated. If the darker blood ejected from the right auricle with each 

 heartbeat is transferred immediately to the perfusion bottle, the heart- 

 beat will soon become feeble and irregular, to be readily restored to 

 normal when this dark blood is shaken up with air or oxygen. 



By artificial perfusion in the manner above described, the automatism 

 of the heart may be restored many hours after death. Partial restora- 

 tion, confined. to the auricles or to that part of the ventricles lying im- 

 mediately adjacent to the large blood vessels, can also be accomplished 

 in the heart of man several days after death, provided death has not 

 been caused by some acute toxic infection such as diphtheria or septice- 

 mia. The Russian physiologist Kuliabko, has succeeded in restoring for 

 over an hour the normal beat of the heart of a three-months-old boy 

 twenty hours after death from double pneumonia, but here again the 

 pulsation returns only in certain parts of the heart. As will be pointed 

 out, the remarkable resistance of the heart muscle displayed in these 

 experiments has been taken as an argument in favor of the myogenic 

 hypothesis for automatic rhythmic power of cardiac muscle, the argu- 

 ment being that nervous structures could not live so long a time after 

 death. The fallacies in this argument are discussed elsewhere. 



RESUSCITATION OF THE HEART IN SITU 



A suitable intracoronary pressure is a sine qua non for the mainte- 

 nance of the heartbeat, and this is a fact of great clinical significance, 

 for it indicates that any attempts to resuscitate a dead animal are cer- 

 tain of failure unless the method is such as will bring a nutrient fluid 

 under a certain pressure to bear on the coronary arteries. Injection of 

 fluid, even of defibrinated blood, into a vein will obviously fail to ful- 

 fill this condition, for the perfusion must be made into an artery so that 

 the fluid is carried down the aorta and thence into the coronary arteries. 



