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SCIENCE PROGRESS 



relative weights of the hearts ; this is what it is in some 

 sparrows, though it is lower than what was found to be the 

 average for four sparrows. Again the hen, which compared 

 with the sparrow would be expected to have a pulse-rate of 



= q8"4 per minute in virtue of its size and its meta- 



I2"2 ^ -r r 



holism alone, would be expected to have one of ^-^^ — = 319 



' ^ 0*42 -^ ^ 



considering also the small size of its heart. If we were to 

 take the carbon-dioxide-output of the thrush as being, as from 

 the size of the bird it is likely to be, about 10 grammes per kilo, 

 per hour, we should have expected its pulse-rate by comparison 

 with that of the sparrow to have been about 666 per minute 

 were it not for the large size of its heart, which makes us expect 

 instead one of only 225 per minute. From what is known of 

 the metabolism of the goose, we should expect its pulse-rate to 

 be about 144 per minute when it is in good condition ; we 

 should expect that of the wild duck to be not much more than 

 half that of the tame, allowing for its carbon-dioxide-output per 

 kilo, per hour being, on account of its smaller size, somewhat 

 less than what Dr. Douglas found it to be in the tame duck 

 whose pulse-rate was recorded. Small hearts and correspond- 

 ingly quick pulses seem, therefore, to be more characteristic 

 of tame birds than of wild, a subject to which we shall have to 



return. 



TABLE II. Mammals 



