Chapter XIII 



WATER BALANCES AND EXCHANGES. 

 RECAPITULATIONS 



§ 100. The materials thus far presented, though serving special 

 interests, may also be considered preliminary to more general con- 

 clusions now to be drawn. These conclusions are partially limited 

 by the voluntary choices of variables and the more involuntary 

 availability of data. But within these limitations a variety of 

 comparisons and a considerable number of inductions may be made. 

 This chapter, in fact, attempts to systematize the materials in such 

 a way as to provide a summarized picture of the physiological regu- 

 lation of water content in animals. Were the study limited to 

 water relations, the presentation might close with it. 



§ 101. Classification of variables 



The scheme followed up to this point may be viewed in terms 

 of variables, classed as follows, largely according to their dimen- 

 sions. Separate divisions are maintained for the quantities most 

 stressed; numerous distinguishable sorts are lumped together in 

 the other divisions {cf. § 5). 



(1) Rates of water exchange or volume changes (Rw or Ry). 



(2) Living units; species, parts of organisms (U). 



(3) Paths of exchange of water or volume (p). 



(4) Changes in properties of whole or of parts (s). 

 (5a) Types of load of water or volume (f ). 



(5b) Amounts of water content or volume (W or V), or load 

 (AWor AV). 



(6) Time and time intervals (t or At). 



(7) Velocity quotients for water volume {k). 



(8) Changes in metabolism and in behavior (M). 



(9) Forces, permeability, size, age (N). 



First I describe how each of the divisions named, when related 

 to others in the list, forms part of the picture of regulation. When 

 the picture is completed, the order in which factors are considered 

 will have had very little influence upon the relations, comparisons, 

 and uniformities found. 



The sorts of variables mentioned may be grouped into continu- 

 ous and discontinuous factors. For, quantities such as water con- 



279 



