SIGNIFICANCE OP PULSE RATE BUCHANAN. 495 



frequencies would be to be expected had we chosen for comparison 

 some other animal. If, e. g., Ave had taken the relation of the mouse 

 to the cat or rabbit we should have expected its pulse rate to be 

 only about 590 or 490, respectively, per minute, which is lower than 

 the average found for six mice. 



Carbon-dioxide output. Pulse rate. Relative heart weight. Pulse rate. 

 980 0.59 732 



- 70 ' 0.79 980 



1435 0.27 490 



205' 0.79 1435 



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 1 is the observed fre- 

 quency 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 haemoglobin 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 life to ascertain what that volume 

 is for any heart; we have had therefore to take the only available 

 data which were at all likely to be a measure of it. 



None of the mammals referred to have pulse rates appreciably 

 higher than those to be expected by comparison with man. All birds, 

 however, so far as we know, have higher frequencies than might be 

 expected when compared with mammals, thus, taking man again as 

 the standard, that for the sparrow would be only 618 instead of 800 

 per minute. 



Carbon-dioxide output. Pulse rate. Relative heart weight. Pulse rate, 

 sparrow 12.2 1423 (K59 618 



man 0.6 70 ' 1.36 1423 



1 If the ox had the same relative heart weight as the bull (0.53 per cent), the pulse 

 rate to be expected by comparison with man would be almost precisely what it actually 

 is in the ox. 



