CIRCULATION. 477 



approximate. Porter l supplied the left coronary artery of the dog with blood 

 diluted one-half with sodium chloride solution (0.6 per cent.) by means of a 

 tube (lumen 2.75 millimeters) inserted into the aortic opening of the left coro- 

 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 cat 

 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. 



Blood-supply and Heart-beat. The relation between the volume of 

 blood passing through the coronary arteries and the rate and force of the 

 ventricular contraction has been studied by Magrath and Kennedy (1896). 

 Variations in the volume of the coronary circulation in the isolated heart 

 of the cat, unless very considerable, are not accompanied by changes in the 

 rate of beat. The force of contraction, on the contrary, appears to be closely 

 dependent on the volume of the coronary circulation (Fig. 125). 



Lymphatics of the Heart. A rich plexus of lymphatic vessels has been 

 demonstrated in the heart. Valuable information concerning the nutrition of 

 the heart could probably be gained by the systematic study of these vessels. 



0. SOLUTIONS WHICH MAINTAIN THE BEAT OF THE HEART. 



The beat of the heart is maintained during life by a constant supply of 

 oxygenated blood. The blood, however, is a very complex fluid, and it can 

 hardly be supposed that all of its constituents are of equal value to the heart. 

 The systematic search for those constituents of the blood which are of import- 

 ance to the nutrition of the heart was begun in Ludwig's laboratory in 1875 

 by Merunowicz. 2 The first step toward the method used by Merunowicz and 

 his successors was taken by Cyon. 3 Cyon tied cannulas in the vena cava 

 inferior and in one of the aortaB of the extirpated heart of the frog, and 

 joined them by a bowed tube filled with serum. The ventricle pumped 

 the serum through the aortic cannula and the bowed tube into the vena 

 cava, whence it reached the ventricle again. The force of the contraction 

 was measured by a mercury manometer which was joined by a side branch 

 to one limb of the bowed tube. 



The frog heart manometer method thus introduced by Ludwig and Cyon 

 has undergone various modifications at the hands of Blasius and Fick, 4 Bow- 

 ditch, 5 Luciani, 6 Kronecker, 7 and others. Blasius and Fick were the first to 

 register changes in the volume of the heart by the plethysmographic method, 

 the organ being enclosed in a vessel filled with normal saline solution and 



1 Porter, 1896, p. 64. 2 Merunowicz, 1876, p. 132. 



8 Cyon, 1867, p. 80. * Blasius, 1872, p. 9. 



5 Bowditch, 1872, p. 139. 6 Luciani, 1873, p. 113. 



7 Kronecker, 1874, p. 174. 



