282 PHYSIOLOGICAL EEGULATIONS 



most parts of organisms, other than the general surfaces of those 

 parts, be they lymph vessels, connective-tissue sheaths, or nuclear 

 membranes. But for cerebrospinal fluid of dog and man (Weed, 

 '38), intraocular fluid (Robertson, '39), and other units, it is gen- 

 erally believed that special surfaces of one-way exchange exist. 



Where paths have been identified it is possible to make con- 

 tributory studies upon specific organs. Thus, the kidneys are 

 often believed by vertebrate physiologists to offer an understanding 

 of many aspects of water regulation. Possibly some information 

 concerning the elimination of water excesses as responses to water 

 loads will eventually come from their separate study; little that 

 relates to loads is recognizable now in analyses of renal function. 

 Ordinary turnover rates are not often regarded as properties of 

 particular organs ; is the distinction between diuresis and normal 

 output made by organisms or by physiologists ? 



(4) Changes of properties (s) with water loads are as numer- 

 ous as the physical and chemical procedures for measuring them. 

 Very many contributions of biophysics and biochemistry furnish 

 data for this particular sort of physiological investigation. Con- 

 tents, pressures, volumes, and dilutions may be distinguished. 

 Actually most measurements of composition now available concern 

 the distributions of water loads within organisms. No doubt a 

 great many properties that have not been measured, also change 

 with water increment; often they were not measured because no 

 theory was conceived to indicate that there might be a particular 

 connection. 



(5a) Types of water increment imposed by the experimenter 

 have diverse consequences. Classification of types might recog- 

 nize: environment for recovery, diet, procedure for loading, path 

 of loading, stationary loads. 



Diverse tolerances, time relations, recovery quotients, and paths 

 are found in the responses to various types. A tentative conclu- 

 sion is that time relations are the most variable features of the 

 responses, among factors so far considered. For ultimately re- 

 covery occurs, and largely by the use of some single path of ex- 

 change, in response to most types of water load. 



(5b) Water contents and various volumes, modified experi- 

 mentally, are evaluated relative to initial or control weight or 

 volume of distribution (AW or AV). In most cases the changes 

 in weight or volume, or in water content relative to analyzed dry 



