GENERAL FEATURES OF WATER EXCHANGES 



191 



t60 



Bipdiium 



-80 -40 +40 +80 



Va+er Load 

 Fig. 111. Rate of net water exchange (% of Bo/hour) in relation to water load 

 (% of Bo) in 7 species of animals. The initial 0.07 to 1.0 hour of recovery is repre- 

 sented, except in Limax and Helix for which a period of 24 hours of recovery prevails. 

 Frog, figure 67; Limax, figure 82; Helix, figure 83; Phascolosoma, figure 87; Bipalium, 

 figure 90; Zoothamnium, figure 92; Arbacia egg (unfertilized), data of Lucke et al. 

 ('31, p. 416). 



Some uniformities that occur in all the instances studied are 

 apparent in the general diagram (fig. 110). 



(1) Net losses occur in water excesses, net gains in water 

 deficits. 



(2) Faster net exchanges accompany larger loads. 



(3) Gains are measurably modified in all displacements from 

 balance, but most in excesses. 



(4) Losses are modified, as compared with turnover, especially 

 in deficits. 



(5) The relative positions of curves for gain and for loss are 

 such that only small ranges of the possible rates of ex- 

 change are utilized at usual water contents. 



(6) Exchanges follow similar patterns, whatever organs and 

 processes are concerned in the exchanges of the particular 

 species. 



(7) At equal positive and negative water loads, recoveries from 

 deficit are more rapid than recoveries from excess. 



The equilibration diagram yields a general and concrete notion 

 of physiological adjustments of water content. As the water con- 

 tent of the organism departs from balance, means of restoration 

 work faster and faster in a direction to bring the content toward 



