TRANSACTIONS OF SECTION I. 815 



3. The ventricle acts on the coronaiy circulation as a force-pump, and not, to 

 any noticeable extent, as a suction-pump. 



D. The circulation through the veins of Thelesius. 



1. The nutrition of the mammalian heart may be maintained through the 

 vessels of Thehesius in a degree sulhcient to give long-continued rhythmic contrac- 

 tions ■while the coronary arteries are empty. 



2. The circulation through the veins of Thebesius is probably an important 

 source of nutrition in hearts in which the coronary arteries have been obstructed 

 by pathological processes. 



3. On the Resistance of the Vasculxir Channels. By Professor K. Hurtule. 



For every scientific investigation of the flow of fluid through a tube or system 

 of tubes a knowledge of the three following factors is necessary : — 



(1) The pressure at thi:- inlet and outlet of the tube (difference = b). 



(2) The velocity of flow, or the quantity of fluid flowing through in an unit of 

 time = Q. 



(3) The resistance offered to the flow. 



Concerning the first two factors in the movement of the blood we have data 

 sufficient for most purposes, but of the third we have no clear conception, since we 

 possess no standard of resistance of the vascular channels. 



The amount of this resistance depends on two factors : — 



(1) The internal friction of the blood. 



(2) The dimensions of the tubular system. 



These two factors must therefore first be determined. 



1. The method used to determine the internal friction of living blood consists 

 in allowing the blood from {e.g.) the carotid of an animal to flow through accu- 

 rately calibrated capillary tubes for about thirty seconds, the quantity, the pres- 

 .sure and the time of flow being accurately measured, the last to within ^ J- second. 



It was proved that this method, in spite of the short period of observation, 

 gives reliable results by determining with it the internal friction of distilled water. 

 The value obtained was the same as that by Poiseuille. 



In the same series of experiments it was also shown that the internal friction 

 can be ascertained even when the pressure varies rhythmically, the outflow bein"- 

 always proportional to the mean pressure, whether the pressure be constant or 

 variable. 



The measurements of the internal friction of the blood of difierent animals by 

 this method gave the following results. The ratio of the internal friction of dis- 

 tilled water at 37° C. (Z- = 4700) to that of the blood is— 



In the dog =1:4-5 (K = 1,045). 

 In the cat = 1 : 4-1 (K = 1 ,140). 

 In the rabbit = 1:3-2 (K = 1,475). 



2. Direct determination of the external resistance by measurement of the 

 dimension of the system of tubes is impossible, since the variation in tonus causes 

 considerable differences in the calibre of the blood-vessels. But if in any par- 

 ticular organ we know (1 j the quantity of blood flov.'ing through in an unit of 

 time ( = Q), (2) the arterial pressure ( = 6), (3) the coefficient of Jnternal friction 

 of the blood ( = A), 



Q = A — ^ — where d is the diameter, and 1 the length of the tube, 



we can, by Poiseuille's law, calculate the dimensions of a tube through which, 

 under the given conditions, the same quantity of blood would flow. Such a tube 



