THE PULSE-RATE IN VERTEBRATE ANIMALS 69 



In the table for mammals a column has been added giving 

 the pulse-rate which, taking both carbon-dioxide-output and 

 relative heart-weight into consideration, we should expect the 

 animal to have compared with man. Man has been chosen as 

 the standard because so many more observations have been 

 made on him that the averages are more likely to be correct 

 than those for the others, with the exception perhaps of the 

 rabbit. Of course somewhat different frequencies would be 

 expected had we chosen for comparison some other animal. If, 

 e.g., we take the relation of the mouse to the cat or rabbit 

 we should expect its pulse-rate to be only about 590 or 490 

 respectively per minute which is lower than the average found 

 for six mice. 



rabbit 



Considering that the rate of formation of carbon-dioxide, 

 the relative heart-size and the frequency of beat, have in the 

 case of nearly all the species been determined by independent 

 observers, it is really rather remarkable how closely the observed 

 and expected frequencies agree. Only in the rabbit and ox^ is 

 the observed frequency considerably (over 30 per cent.) lower 

 than was to be expected from that of man. It is probably also 

 about 25 per cent, lower in the pig, though we have not yet the 

 data for knowing what to expect for the pig. A higher haemo- 

 globin percentage in the blood would compensate for what 

 seems to be otherwise too slow a blood-supply to enable the 

 oxygen loss to be made good, but although we know this 

 percentage to be higher in the ox than in man, it is in the 

 rabbit a good deal lower than in man. Since in the rabbit at 

 any rate the averages are likely to be correct, we have probably 

 still to seek for some other factor which enables the supply of 

 oxygen to meet the demand. But it must be remembered that 

 the relative heart-weights may not run strictly parallel with the 

 volumes of blood expelled at each systole in the different species. 

 Unfortunately we do not know and it would be difficult during 



' If the ox had the same relative heart-weight as the bull (o'53 per cent.), the 

 pulse-rate to be expected by comparison with man would be almost precisely what 

 it actually is in the ox. 



