CIRCULATION. 185 



nary artery and connected with a reservoir placed 150 centimeters above the 

 heart. In one dog, weighing 11,500 grams, 318 cubic centimeters flowed 

 through in eight minutes. In a second dog, weighing 9500 grams, 114 cubic 

 centimeters passed through in four minutes. In the isolated heart of the caf 

 strong and regular contractions are made on a circulation of about 4 cubic 

 centimeters per minute, or even less, through the coronary system. The 

 quantity passing through the veins of Thebesius into the left auricle and 

 ventricle is very slight. 



The supply of blood to the heart-muscle is modified by ventricular con- 

 traction, not only in that the mean blood-pressure in the aorta is a function 

 of the force of the heart-beat, but directly by the compression of the intra- 

 mural vessels during systole. Thus, when a piece of the mammalian ven- 

 tricle is kept beating by supplying it with defibrinated blood through its 

 nutrient artery at a constant pressure, each beat can be seen to force the blood 

 out of the severed vessels in the margin of the fragment. The effect of the 

 contractions on the contents of the intramural vessels can also be demon- 

 strated in the living animal by incising a vein, or a ligated artery on the 

 distal side of the ligature, and slowing the heart by stimulation of the vagus. 

 At each systole of the ventricle blood is forced from the vessel. More- 

 over, lessening the frequency of contraction diminishes the volume of the coro- 

 nary circulation — i. e., the outflow from the coronary veins, as may be shown 

 in a record similar to that illustrated by Fig. 40. It is conceivable that 

 the emptying of the intramural vessels by the contraction of the heart may 

 favor the flow of blood through the heart-walls in two ways: first, by the 

 diminished resistance which the empty patulous vessels should offer to the 

 inflow of blood from the aorta when the heart relaxes ; and, secondly, by 

 the suction which might accompany the sudden expansion of the compressed 

 vessels — expanding either by virtue of their intrinsic elasticity, or because 

 of the pull of the surrounding tissues upon their walls, as the heart quickly 

 regains its diastolic form. The problem thus raised may be attacked by sud- 

 denly connecting the distal portion of a coronary artery in the strongly beat- 

 ing heart of the living animal with a small reservoir <>f normally warm de- 

 fibrinated blood at the atmospheric pressure. The connection can be made 

 through a cannula tied into the artery (ramus descendens of the dog) or 

 through a tube passed into the left coronary artery by way of the innominate 

 artery and aorta. If each compression of the deeper branches of the artery 

 were followed by an expansion sufficient to cause a noteworthy suction, the 

 blood in the reservoir should be drawn into the artery, for this blood is the 

 sole source of supply throughout the experiment, as the " terminal " nature 

 of the coronary arteries prevents any material backflo\n from the distal 

 branches. The results of these experiments showed that no appreciable suc- 

 tion can be demonstrated in the larger coronary arteries, even when a very 

 sensitive minimum valve is interposed between the artery and the reservoir 

 in order to prevent the possible masking of the suction b\ rising pressure 

 accompanying the contraction of the ventricle. It is, therefore, necessary 



