NATURAL RHYTHM. 



167 



with the greatest regularity 33 times per minute in 

 water kept at 34°; but on transference to water 

 kept at 49'", the contractions always became irregular, 

 in respect (a) of not having a perfectly constant 

 rhythm, and (h) of exhibiting frequent pauses, which 

 was never the case in colder water. The rate of 

 rhythm in the warmer water varied from 37 to 49 ; 

 and as in these observations no allowance was 

 made for the occurrence of the pauses, the actual 

 rate of rhythm during the swimming motions was 

 about 60 per minute. The following are some 

 sample observations in the case of this specimen : — 



This rate continued quite regularly for a quarter 

 of an hour, when the observation terminated. 



It might naturally be supposed that when the 

 alterations of temperature between 34° and 49° 

 produce such marked effects on the rhythm, still 



