PARAMOECIUM POSSESSING EXTRA VACUOLES 307 



. b. Resistance 



This race has proved itself to be more resistant to all the ab- 

 normal conditions it has been subjected to than have the common 

 animals. 



Heat. Dr. Jacobs has found that under conditions where the 

 ordinary paramoecia are killed at temperatures of 40° to 42° C. 

 the race in question may survive an exposure to 44°. Animals 

 that have been living in a hay infusion to which a small per- 

 centage of sea salt has been added resist high temperatures for 

 very much longer periods of time than are paramoecia taken 

 from pure hay infusion. My experiments along this line are, 

 as yet, not sufficiently extensive to base conclusions. 



Cold. A few animals of the multi-vacuoled race withstood an 

 air temperature of 



1° to 2° for 45 hours 

 -3° to -4° for 2| hours 



The common race was killed in the first case between five and 

 thirty hours and in a trifle over an hour in the second experi- 

 ment. In this time, although ice crystals were formed, the 

 fluid did not freeze solid at this low temperature. 



Distilled water. Mr. Mitchell Carrol, of the Zoological Lab- 

 oratory of the University of Pennsylvania, has maintained this 

 race of paramoecium in distilled water for fifteen generations, 

 covering a period of forty-four days. In similar experiments of 

 my own these animals showed the same ability to live in distilled 

 water. 



c. Rate of vacuole contraction 



A few observations on the rate of vacuole contraction under 

 varying conditions have been made on this new race of Para- 

 moecium to determine whether there is any essential difference 

 between this and the common stock. Two methods have been 

 employed. In the first method each vacuole as it contracted 

 was called off to an assistant who noted the time. Several ob- 

 servations were made on each vacuole and then the records 

 obtained for each vacuole were averaged. In all forty-four ani- 

 mals were studied at 23°C. with an average of three observations 

 per vacuole per animal. 



