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 (b) 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 :— 
Temperature of water (Fahr.) | Number of pulsations. Seconds of rest. 
a ee 41 5 
= eel toes 49 4 
Transferred to 31° ... wee 33 0 
= ey eee 33 0 
n = 5 the Jae 33 0 
Bs 2 keds iinet 33 0 
Transferred to 19° ... ... | 45 4 
Z ee ea ay 39 10 
= eee eee em 37 15 
Transferred to 31° 4... awe 20 0 
- * ee cue 30 0 
» Am Seateeionc oo 0 
” 9 33 0 
9 ”? 33 0 
= = ‘ ; 33 9 
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 
