154 Chapter IX 



flow. The alterations in the rate of flow keep company with the 

 C0 2 output and like it lag after the changes in pulse rate. The 

 simultaneous "hysteresis" of the vascular dilatation and of the CO 2 

 production shows that the increased blood flow caused by increased 

 activity is not due to a mechanical propulsion but to a chemical event. 

 In order to test the effect of metabolites on the coronary circula- 

 tion more completely Dixon and I determined to induce partial 

 asphyxia by restriction of the respiratory orifice of the perfusing 

 animal. The carbonic acid accumulates in the blood and as the 

 arterial blood gets darker the flow through the coronary vessels 

 of the supplied heart increases, at the same time the heart beat 

 slows it becomes less- efficient (14) (the call for oxygen being unabated 

 and tending if anything to increase). 



Heart of puppy perfused from Dog. 



The occlusion of tracheal tube commenced between periods I and II and ended 



after period III. 



CO 2 used per g. 

 per min. c.c. 



043 

 035 

 008 

 012 



Kitten's heart perfused from Cat. 



I 12-1 26-6 1-75 -010 -005 



II 5-4 41-1 5-7 -Oil 002 



Whilst the dilatation took place at the height of asphyxia this 

 experiment differed from those shown in Fig. 81 in that the C0 2 

 output in this period was particularly small. A possible explanation 

 of this (though not the only one) was that the asphyxiated blood 

 contained products of incomplete oxidation which likely enough 

 were more active than C0 2 . Indeed Verzar has since shown that the 

 blood coming from the titanised gastrocnemius contains measurable 

 quantities of acid products* 151 . We performed further experiments 

 in which the effect of C0 2 was eliminated whilst that of other products 

 remained. The asphyxia was produced by making the perfusing 

 animal breathe a mixture of nitrogen and oxygen which became 

 increasingly poor in the latter. When the oxygen sank to about 

 4 % the heart beats began to fail. Period II corresponds to this. 



Oxygen in CO 2 in Blood flow 2 used CO 2 prod. 



Period art. blood / art. blood / per min. per g. per min. per g. per miu. 



I 15-4 35 8 -036 '025 



II 2-1 36-2 48 -033 



