476 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



of the dog's heart has been supposed impossible. 1 McWilliam, however, has 

 seen a number of regular beats after the termination of fibrillary contraction. 2 

 Recent results suggest that fibrillary contractions even in the highest verte- 

 brates may be removed by establishing an artificial circulation of defibrinated 

 blood through the coronary arteries. 



Closure of the Coronary Veins. Closure of all the coronary veins in 

 the rabbit produced fibrillary contractions after from fifteen to twenty minutes 

 had passed. 3 Their closure in the dog is said to be without effect 4 a negative 

 result perhaps to be explained by the fact that a portion of the coronary blood 

 finds its way to the cavities of the heart through the vense Thebesii. 5 



Volume of Coronary Circulation. Bohr and Henriques, 6 taking the 

 average of six experiments on dogs, found that 16 cubic centimeters of blood 

 passed through the coronary arteries per minute for each 100 grams of heart 

 muscle. The quantity passing through both coronary arteries varied in dif- 

 ferent animals from 20 to 64 cubic centimeters per minute ; the quantity 

 passing through the left coronary artery varied from 22.5 to 60 cubic centi- 



FIG. 125. Diminution of the force of contraction of the ventricle of the isolated cat's heart in con- 

 sequence of diminishing the supply of blood to the cardiac muscle : A, blood-pressure at the root of the 

 aorta, recorded by a mercury manometer ; B, intra- ventricular pressure-curve, left ventricle : the indi- 

 vidual beats do not appear, because of the slow speed of the smoked surface ; C, time in seconds ; D, the 

 number of drops of blood passing through the coronary arteries, each vertical mark recording one drop. 

 As the number of drops of blood passing through the coronary arteries diminishes, the contractions of 

 the left ventricle become weaker, but recover again when the former volume of the coronary circula- 

 tion is restored. 



meters per minute. The hearts weighed from 51 to 350 grams. The method 

 which Bohr and Henriques found it necessary to employ placed the heart 

 under such abnormal conditions that their results can be regarded as only 



1 Cohnheim and v. Schulthess-Rechberg, 1881, p. 519; Tigerstedt, 1895, p. 546; and others. 



2 It is not quite clear whether McWilliam refers to fibrillary contractions produced by 

 closing a coronary artery or to those which follow strong faradic stimulation of the ventricle 

 (1887, p. 299). 



3 v. Bezold and Breymann, 1867, p. 299. * Michaelis, 1894, p. 291. 



5 Gad, 1886, p. 382. 6 Bohr and Henriques, 1895, pp. 233-236. 



