THE PULSE-RATE IN VERTEBRATE ANIMALS 71 



Echidna, although it fails, makes the attempt for the greater 

 part of the year, and the oxygen consumption in the individual, 

 at any given external temperature, seems to some extent to 

 vary inversely with the size, judging from the determinations 

 made by Dr. Martin of the carbon-dioxide-output per unit 

 weight and time in three individuals (10). Those placental 

 mammals which do not regulate their temperature the whole 

 year round do not succeed much better than Echidna when they 

 make the attempt, especially on first awaking from hibernation. 

 In some of them the temperature seems to remain lower than 

 in other placental mammals. The rectal temperature of a bat, 

 for instance, may be only 30° C. when it is wide awake and 

 active (16). The low temperature in such cases seems again to 

 be due to the production of heat being small in comparison 

 with other mammals of the same size. Thus in an active bat 

 weighing about 20 grms. the carbon-dioxide-output per kilo, per 

 hour was found to be only about 4*5 grms. and therefore con- 

 siderably less than in a mouse. If we may take this as a 

 measure of the demand for oxygen in an active bat, the heart 

 need not beat with a frequency of more than 250 per minute 

 to supply the demand, seeing that the heart of the bat, as we 

 happen to know from two independent sources (3) and (16), 

 weighs as much as V2 per cent, of the body-weight, and is 

 therefore relatively larger than that of the mouse, A small 

 dormouse on the other hand, in which the carbon-dioxide-output 

 may be as much as 20*4 grms. per kilo, per hour when awake 

 (16), we should expect to have a pulse-rate of over 1000 per 

 minute, even if it has as large a heart (relatively) as a bat. It is 

 said to have a pulse-rate of only 16 or 14 per minute when 

 hibernating (i6a). 



Before going further a few words should be said about the 

 method of ascertaining the frequency of the beat in small warm- 

 blooded animals. It would be difficult to count a frequency 

 of over 300 a minute or to record any mechanical movements of 

 the heart when they are so rapid in the living intact animal. 

 We can however make use of the fact, the meaning of which 

 is not yet sufficiently understood (5) and (6), that the electrical 

 changes, accompanying muscular activity produce, with each 

 ventricular systole in the case of the hearts of mammals, birds 

 and certain if not all reptiles, two electric fields, the one of 

 which pervades the anterior, the other the posterior part of the 



