152 Chapter IX 



the perfused heart. This line of argument does not account for the 

 changes in blood flow. The drugs were always injected in the tube 

 leading straight to the perfused heart and in such small quantities 

 that whilst they affected it profoundly they had little or no effect 

 upon the general circulation of the perfusing animal. For example 

 take Exp. 6 (Fig. 81), in it there are two periods one before and one 

 after the activity of the perfused heart has been reduced by the in- 

 jection of 20 minims of chloroform water into the tube leading to the 

 perfused heart. In Fig. 82 both the tracing of the perfused heart 

 and that of the general arterial pressure are shown in the two periods 

 of the experiment. The general arterial pressure is scarcely altered, 

 the metabolic activity of the heart is much reduced. This reduction 

 is shown by the reduction in amplitude and frequency of the heart's 

 beats as seen in the tracing ; it is shown also by the change in the 

 metabolism. 



Period I Oxygen taken in C0 2 given out 



Before chloroform injection ... 3 c.c. per min. 8-8 c.c. per min. 



Period II 



After chloroform injection ... '37 1'9 ,, 



As the actual effect of the chloroform in the coronary vessels them- 

 selves would be dilatation, we might therefore have expected that, 

 other things being equal, there would have been a more rapid flow of 

 blood through the coronary system of the perfused heart. Never- 

 theless this was not the case, the blood flow in the first period was 

 30 c.c. per minute, in the second 9 c.c. 



Now that the effects of changes in the general arterial pressure 

 have been excluded and in some experiments the local effect of the 

 drug upon the vessels, what possibilities remain ? The direct action of 

 drugs on the vessels of the perfused heart may be still further elimin- 

 ated, for in some of our experiments the rate of flow was not altered as 

 the result of drugs but as the result of stimulation of the vagus of the 

 perfused heart ; this clearly does not affect the general arterial pres- 

 sure of the perfusing animal, nor is it claimed that the vagus carries 

 constrictor (fibres to the coronary vessels ; therefore the changes in 

 blood flow which we get as the result of vagus stimulation cannot be 

 regarded as due to either of the causes which we have considered. 

 The rate of blood flow however follows the C0 2 output very closely. 



In the experiment, a tracing of which is given, there were three 

 periods : (1) before vagus stimulation, (2) during vagus stimulation, 

 and (3) after vagus stimulation. 



