146 



PHYSIOLOGICAL KEGULATIONS 



waters. In the early efforts to analyze the factors of water trans- 

 fer and to rationalize the quantitative relationships, it was impor- 

 tant to minimize the irregularities found. In a later analysis it is 

 useful to realize that one permeability coefficient h does not charac- 

 terize all exchanges of water in any one species. 



§ 52. Feeshwatek Zoothamnium 



Zoothamnium, a genus of ciliate protozoa, allows independent 

 measurements of output through contractile vacuoles and of coinci- 

 dent body volume (Kitching, '38). Moreover, both initial states 

 and steady states may be investigated. Two species are examined, 

 one of which lives in fresh water, the other in sea water. 



When individuals of the first species are put into one of two 

 chosen media, either a negative or a positive water load is estab- 



800 1 



e 600 



u 



2 



6 



400 



ZOO 



Intake 



Freshwater Ciliate 

 Zoothamnium 



-30 



-20 



Output- 



MO 



Water Load 



Fig. 92. Initial rate of water exchange (% of Bo/hour) in relation to water load 

 (% of Bo). Zoothamnium, freshwater peritrich protozoan, at 15° C. A, an individual 

 returned from 0.05 M sucrose solution to tap water. B, an individual returned from 

 0.005 M sodium cyanide, which had inhibited contractile vacuolar activity, to tap water. 

 Each point represents recovery during a period of 0.07 to 0.17 hour. Data of Kitching 

 ('38). 



lished. On transfer from those media to the control medium (fresh 

 water), water is exchanged at the rates shown in fig. 92. The total 

 water loss is the volume measured as leaving the body through 

 vacuoles, while the gain is the change of volume plus the water loss. 

 Measured in change of volume alone, the rate of net gain in deficits 

 is much greater than the rate of net loss in excesses. It is uncer- 

 tain whether this contrast in positive and in negative loads is gen- 



