RATE OF THE HEART-BEAT IN A CRUSTACEAN. 243 



gated the influence of temperature upon the rate of the heart- 

 beat and found that the rate of the beat in the heart of the ter- 

 rapin (Clemmys inannoratii) is almost exactly doubled by ten 

 degrees rise in temperature between the temperatures 10 C. and 

 32.5 C. at lower temperatures the rate is more than doubled 

 by a rise of 10 while at higher temperatures the rate is some- 

 what less than doubled by the same rise in temperature. Loeb 8 

 has found that the velocity of artificial maturation in the eggs of 

 Lottia is more than doubled by raising the temperature from 8 

 C. to 1 8 C. Other investigations on the influence of tempera- 

 ture upon biological phenomena are being carried out in this 

 laboratory. These observations do not prove that the above- 

 mentioned biological phenomena are entirely chemical in char- 

 acter, but they afford indication that chemical reactions are 

 involved although not to the exclusion of possible concurrent 

 physical changes. 



3. It appeared to me of interest, in connection with experiments 

 on the influence of electrolytes on the rate of the heart-beat, of 

 which an account will appear at an early date, to ascertain the 

 influence of temperature upon the rate of the heart-beat in the 

 transparent fresh-water crustacean Ceriodaphnia (?). The organ- 

 ism, after washing in tap-water, was laid in a drop of tap-water in 

 the depression on the glass top of an Englemann gas-chamber, 

 the temperature being regulated by running warm or cold water 

 through the chamber. A thermometer was fitted into the chamber 

 so that the bulb lay directly under the depression in which the 

 organism was placed. A few minutes was always allowed to 

 elapse before the rate of the beat was registered in order to allow 

 the organism to attain the same temperature as the bulb of the 

 thermometer. The beats at room-temperature and at higher tem- 

 peratures are so rapid that they cannot be counted but have to 

 be recorded by tapping a key which completes a circuit includ-- 

 ing a signal-magnet, which thus registers a mark upon a revolv- 

 ing drum for every beat, the time being taken with a stop-watch. 



4. The following are the experimental results. 



8 University of California Publications, Physiology, Vol. 3, p. I. 



