438 THE DYNAMICS OF CARDIAC ACTION. 



meshes of which, elongated and parallel to the muscular fascic- 

 uli, are connected by short branches, which give each mesh the 

 appearance of a parallelogram. When these vessels cross the 

 spaces of Henle, they are covered, on the external surface, with 

 flat connective-tissue plates/' Pratt's observation not only in- 

 cludes the analogy between the human lung and that of the 

 frog, but also with that of the cat, a mammal. Under these 

 conditions, it becomes clear that in man, also, the heart-muscle 

 may be regarded as a sponge-like structure, the contractile elements 

 of which are nourished and supplied with working energy by 

 substances in the blood-plasma. 



What is the role of the blood of the coronary arteries in 

 the functions of the heart? This may perhaps be traced by 

 analyzing the effects of ligation of these arteries upon these 

 functions. Porter 15 refers as follows to the experimental work 

 in this connection: "The frequency of arrest after ligation is 

 in proportion to the size of the artery ligated, and hence to the 

 size of the area made anaemic, and is not in proportion to the 

 injury done in the preparation of the artery. The circumflex 

 and descendens may be prepared without injuring a single mus- 

 cle-fiber, yet their ligation frequently arrests the heart, while 

 the ligation of the arteria septi, which cannot be prepared with- 

 out injuring the muscle-substance, does not arrest the heart. 

 It is, moreover, possible to close a coronary artery without me- 

 chanical injury. Lycopodium-spores mixed with defibrinated 

 blood are injected into the arch of the aorta during the mo- 

 mentary closure of that vessel and are carried into the coronary 

 arteries: the only way left open for the blood. The lycopodium- 

 spores plug up the finer branches of the coronary vessels. The 

 coronary arteries are thus closed without the operator having 

 touched the heart. Prompt arrest, with tumultuous fibrillary 

 contraction, follows." 



If the plasma that reaches the heart by way of the Thebe- 

 sian channels can sustain both its nutrition and its contractions, 

 how can such results as these be accounted for? The sudden 

 arrest of the heart's action by plugging the coronary arteries 

 certainly points to a predominating function, and, more than 

 this, to a function of which they are alone the sources of blood- 



18 Porter: Loc. cit. 



