The call for oxygen by the heart 



89 



with blood but with oxygenated Locke's solution. Here again little 

 explanation is needed beyond the statement of the general principle : 

 the Locke's solution circulated round a closed circuit in which was 

 placed among other things (1) the heart which deoxidised the solution, 

 and (2) a chamber from which the fluid could take up another stock 

 of oxygen before returning to the heart ; the supply of oxygen in 

 this chamber was kept up by the admission of fresh quantities of the 

 gas from a reservoir, and the quantity of the gas so admitted was 

 measured. In this way it was possible to find out how much gas the 

 heart was using over considerable periods of time and thus to rid the 

 calculations of momentary fluctuations. The method appears to give 

 reliable results for time intervals of ten minutes and over. 



Of the results which Rohde obtained I will first refer to that of 

 a heart which, at the same initial pressure, was made to beat both 

 isotonically and isometrically. 



The more interesting and important part of the work may be best 

 gathered from the account of one of the 177 experiments which 

 Rohde performed. 



The functional activity of the heart was altered by altering the 

 pressure in the pressure bottle. 



Fig. 53 shows a series of tracings from a heart. The heart was 

 beating isometrically ; the tracings represent the changes of pressure 

 as registered by Frank's manometer. Take the first portion which 

 shows heart beats, what information does it give ? It tells (1) the 

 frequency of the beats, which is 159 per minute, (2) the initial pressure, 

 which is 35 mm. of mercury, (3) the maximal increase of pressure, or 

 as Rohde calls it the pulse pressure, which is 97 mm. In the other 

 tracings each one of these is changed. The question then is, upon 

 which of these does the oxygen used by the heart depend? The 

 answer is, that it does not vary directly with any one, but with the 

 product of the frequency and the maximal increase of pressure. 

 To put the thing in another way, if Q is the oxygen used, T the 



