The regulation of the supply of oxygen to the tissues 151 



The activity of the heart was altered very much in degree in 

 different experiments, and in various ways, by the administration 

 of adrenalin, pilocarpine, atropine, chloroform, vagus stimulation, 

 etc. ; one general fact which emerged from the experiments was the 

 close relationship between the output of carbonic acid and the rate 

 of flow of blood. This is shown for the series of experiments in 

 Fig. 81. The correspondence between the two is extraordinarily 

 complete. It is incredible that such a coincidence should happen 

 merely by chance, but whilst it must be admitted, I think, that the 



I II 



FIG. 82. Upper tracing represents record of puppy's heart. Lower tracing = blood 

 pressure of the perfusing animal. Period I = normal. Period II shows the effect of 

 injecting 1'2 c.c. of CHC1 3 water. The signal mark represents the time during which 

 the sample of blood was taken. 



blood flow and the CO, output are in some way related, an analysis of 

 this relationship is necessary before the assertion that the change in 

 the cross-section of the coronary vessels was caused by the changes 

 in the metabolic activity of the perfused heart is warranted. 



The other possibilities are as follows : 



Drugs which tend to increase the activity of the perfused heart, 

 adrenalin for instance, would also tend to increase the activity of 

 the perfusing heart ; this would tend to raise the general arterial 

 pressure in the perfusing animal and so alter the blood flow through 



