428 THE CONTRACTILE VACUOLE 



amount of fluid expelled in three experiments, each of 10 minutes' dura- 

 tion, was 45,000 cubic micra; and the average amount of water taken 

 into the organism with food was 11,700 cubic micra, or about one- 

 fourth the total amount expelled. In animals not feeding, the entire 

 amount of fluid expelled entered the body otherwise than with food. 

 Basing his theory on the work of Nirenstein as well as on his own 

 observations, Eisenberg concludes that water penetrates the body by way 

 of the peristome, even when a food vacuole is not in process of forma- 

 tion. It was further observed that an increase in the osmotic pressure 

 of the exterior medium results in a decrease in pulsation frequency, and 

 that equi-osmotic solutions of different chemicals may cause different 

 degrees of slowing. 



Fortner (1926) concludes, largely on the basis of theoretical con- 

 siderations, that the vacuole operates for the preservation of vital cell 

 turgescence, since there must be an accumulation of water in the proto- 

 plasm because it is surrounded by a membrane impermeable to water 

 and aqueous solutions. 



Eisenberg (1929) investigated the relationship between the osmotic 

 pressure and the pulsation frequency of the vacuole in Balantidium 

 entozoon. He found that the frequency of the formation of vacuoles 

 depends on the osmotic pressure, and is all the greater the more the 

 pressure is reduced below that of the usual environment. A pulsation 

 frequency accelerated by the removal of the organism to a medium 

 of lower osmotic pressure does not remain accelerated, but returns to 

 normal after a certain period of time. The rapidity and extent of this 

 return to normal are proportional to the osmotic pressure of the medium. 



Frisch (1935) was unable to adapt Paramecium caudatum and P. 

 multimicronucleata to sea water, the organisms dying when the concen- 

 tration reached 40 percent. However, among other marked changes in 

 ithe organisms was a pronounced decrease in pulsation frequency of the 

 vacuoles. 



Day (1930) concludes from his observations on Spirostomum and 

 Paramecium that the vacuole is a hydrostatic organelle, which functions 

 also in elimination of metabolic wastes. He found conductivity water 

 to increase the size, number, and rate of pulsation of vacuoles. The 

 lowering of the temperature of the culture medium slows the organisms 

 and retards the contraction rate of vacuoles, while the raising of the 



