The call for oxygen by the heart 87 



has been made clear by Fletcher (9) that an evolution of CO 2 follows 

 from a production of lactic acid in the frog's gastrocnemius. 



Dixon and I came to the conclusion that the irregularity was 

 only apparent and that in reality the changes in C0 2 production 

 lagged somewhat in time after the changes in the oxygen intake; 

 this "hysteresis" of C0 2 was also apparent in the kidney (10) and 

 the intestine (11) , and as we said above it has been confirmed in the 

 heart by Evans. 



Evans was interested in the effect of increased activity, not only 

 on the call for oxygen, but also on the respiratory quotient of the beat- 

 ing heart. In a calculation of the ratio of the * ,, - by the 



O 2 taken in 



organ, this carbonic acid " hysteresis " proved fatal to the application 

 to his problem of the method Dixon and I had employed. To obtain 

 valid data it was necessary to integrate the whole of the oxygen 

 taken in and of the CO 2 given out over a long time (20 minutes). 

 For this purpose Evans had recourse to an ingenious device which 

 likely enough will prove useful for other purposes. He made a 

 heart-lung preparation something similar to that used by Stolnikoff 

 for measurement of the output of the heart. He then circulated air 

 through the lungs by an artificial respiration apparatus, and measured 

 the amount of oxygen taken up and of CO 2 given out. After an 

 allowance had been made for the gaseous exchange of the lungs 

 themselves, these data furnished the respiratory quotient of the heart. 



One of the merits of this preparation consists in the ease with 

 which the work performed by the heart can be varied. Taking the 

 work as being practically (the output) x (the pressure against which 

 the heart is working), the work may be increased in either of two 

 ways: (1) by feeding the right auricle with more blood, and (2) by 

 increasing the resistance in the aorta. Evans obtained an absolute 

 rise in the oxygen intake and in the CO 2 output when extra work was 

 thrown upon the heart, but if the heart were in good condition he 

 obtained a fall in the gaseous exchange per kilogram-metre of work 

 performed and also a fall in the respiratory quotient. Judged as a 

 machine the efficiency of the heart was extremely low from two to 

 ten per cent. 



At the risk of going outside the title of my book I cannot refrain 

 from an allusion to the work of Rohde, despite the fact that he worked 

 on an excised heart perfused with Locke's solution ; for on the work 

 of Rohde I am an enthusiast. His technique may be considered 



