474 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



FIG. 124. Showing fall in arte- 

 rial pressure and diminished out- 

 put of left ventricle in consequence 

 of the ligation of the circumflex 

 artery. The curve reads from left 

 to right. It is one-half the original 

 size. The upper curve is the pres- 

 sure in the carotid artery. The 

 unbroken line is atmospheric pres- 

 sure. The next curve is the meas- 

 urement of the outflow from the 

 left ventricle, each rise and each 

 fall indicating the passage of 50 

 c.cm. of blood into the aorta. The 

 lower line is a time-curve in sec- 

 onds. At * the circumflex artery 

 was ligated (Porter, 1896, p. 51). 



occasionally the frequency is increased. Both ven- 

 tricles as a rule cease to beat at the same instant. 

 The work done by the heart, measured by the 

 blood thrown into the aorta in a unit of time, is 

 lessened by ligation when followed by arrest : (see 

 Fig. 124). 



The Exciting Cause of Arrest. There are 

 two opinions concerning the exciting cause of the 

 changes following closure of a coronary artery, 

 some investigators holding for anaemia and others 

 for mechanical injury of the cardiac muscle or its 

 nerves in the operation of ligation. The latter 

 base their claim on the frequent failure of ligation 

 of even a main branch to stop the heart ; on the 

 fact that the heart of the dog has been seen to 

 beat from 115 to 150 seconds after the blood-pres- 

 sure in the aorta was so far reduced, by clamping 

 the auricle and opening the carotid artery, as to 

 make a continuance of the coronary circulation 

 very improbable; 2 on the revival of the arrested 

 heart by the injection of defibrinated blood into 

 the coronary arteries from the aorta, by which 

 means the dog's heart and even the human heart 

 has been made to beat again many minutes after 

 the total arrest of the circulation, 3 it being as- 

 sumed, incorrectly, that the dog's heart cannot be 

 made to beat after arrest with fibrillary contrac- 

 tions ; and, finally, on the arrest with fibrillary 

 contractions which some experimenters have caused 

 by mechanical injury to the heart. 4 



To sum up, the argument in favor of explain- 

 ing arrest with fibrillary contractions simply by 

 the mechanical injury done the heart in the pro- 

 cess of ligation consists of two propositions : first, 

 that anaemia without mechanical injury does not 

 cause arrest with fibrillary contractions ; and sec- 

 ond, that mechanical injury without anaemia does 

 cause arrest. 



Against the second of these propositions must 

 be placed the extreme infrequency of arrest from 

 mechanical injuries. In more than one hundred 



1 Porter, 1896, p. 52. 



2 Tigerstedt, 1895, p. 87 ; Michaelis, 1894. 



3 Langendorff, 1895, p. 320; H6don and Gilis, 1892, 

 p. 760. 4 Martin and Sedgwick, 1882, p. 168. 



