The call for oxygen by the heart 



85 



Gas per gram per min. 



'- ' s^ 



Oxygen Carbonic acid 



Period I. Before stimulation 0'014 c.c. 0-038 c.c. 



,, II. During ,, 0-009 c.c. 0-005 c.c. 



,, III. After ,, 0-022 c.c. 0015 c.c. 



It is sufficiently evident from the examples which we have given 

 that obvious changes in the activity of the heart run, roughly speaking, 

 part passu with changes in the call for oxygen. 



There are two remaining points in the research which may here 

 be considered and which I am inclined to emphasise more strongly 

 than I did at the time, in view of the fact that they have both since 

 been confirmed by the work of Evans (7) . 



i II 



FIG. 50. Record of puppy's heart. Period I shows the condition during the incompetence 

 of the aortic semi-lunar valves (i.e. the isometric condition). Period II shows the 

 recovery after a tube had been introduced into the left ventricle (i.e. the isotonic 

 condition). 



The first deals with a case in which the change in the activity of 

 the heart is not evident. It is distended with blood to such an 

 extent that it cannot contract. The condition of the heart may be 

 expressed in more than one way ; in our paper we stated that it was 

 undergoing isometric contractions : in the light of the more recent 

 work of Rohde ((i) and of Hill (S) , to which we shall shortly refer, we 

 would say that each beat expended itself simply in a change of 

 tension and not in a change of form. 



The question then that was thus accidentally forced upon us was 

 whether, in the absence of evident contractions, there was increased 

 oxidation. The following is our description of this experiment: 

 " The cavities on the left side of the heart were much enlarged. 

 The heart was endeavouring to contract but the resistance to the 



