GENEEAL FEATURES OF WATER EXCHANGES 205 



chemical conditions, physiological states, anatomical units, and 

 physiological outcomes. 



The number of varieties of water load explicitly mentioned in 

 the dog alone is about 15 (chapter III). The number of varieties 

 of At considered is about 12, even though an arbitrary man-made 

 clock is used in obtaining them all. Among 15 kinds of AW with 

 12 kinds of At, a product of 180 indicates the combinations that 

 might be studied if I were concerned merely in rearranging 

 coordinates. 



Uniformities among the water relations studied are features 

 common to all the organisms investigated, while quantities limited 

 to alimentary tracts or to osmosis do not apply in organisms devoid 

 of them. In this way the account comes to consist of the materials 

 of general physiology, and only further inquiry will show just how 

 general the present conclusions are. Some of the recognizable 

 features are : (1) The species studied lose water faster when water 

 content is high and gain water faster when content is low. {2) 

 Rates of gain and of loss are equal at one water content (balance), 

 to which the organism recurs after each disturbance and at which 

 alone exchanges rest. (5) Rates of water exchange are correlatives 

 of water content. They are not always functions of the time 

 elapsed since displacement or since recovery began. (4) Incre- 

 ments of water content exceeding 10 per cent of the water already 

 present are tolerated by all species tested. Certain other generali- 

 zations are mentioned above in § 72. 



