WATER BALANCES AND EXCHANGES 285 



time, and from inferring' that what is true in rabbit holds equally 

 in man. In time, however, the wishful reasonings by which the 

 particular pairs of variables were chosen will probably disappear, 

 and the remaining {n-2) quantities become conspicuous by the 

 absence of data concerning them. 



While figure 131 furnishes an exact description of the water 

 relations in one kind of organism under one set of conditions, the 

 scheme of description is general, for it applies to any organism, 

 group, or parts. From many such descriptions the range of values 

 over which the quantities vary may be found. No other test of the 

 generality of correlations with water load seems to exist. 



<§ 104. Proceduees or steps used 



The first step in any investigation is to select kinds of observa- 

 tions or measurements that are to be made ; very often, of course, 

 that is done subconsciously. The second step, grouping those kinds 

 into classes of variables, seems to be more successful if done with 

 all the consciousness that can be brought to bear. Thereafter, the 

 correlations among classes of variables are made in the light of 

 whatever hypotheses prompted the investigation, largely by stand- 

 ardized methods. A set of measurements, tests, and conditions are 

 chosen ; they are classified ; and the inevitable coincidences among 

 them are ascertained. Any desired degree of completeness in 

 characterizations may be attained, such that finer and finer con- 

 trasts can be found among diverse species or individuals or states. 



The specific steps in arriving at this stage of physiological 

 description of water relations may be set down as follows : 



(1) Select by some reproducible criterion a group of individuals 

 or parts for experimental tests (U). 



(2) Select one or more modes of imposing water excesses or 

 deficits in graded amounts (f ) . Fix the conditions for maintenance 

 of the individuals and for recovery from the increments. 



(3) Follow in time (t) the changes of water content or volume 

 (W or V), and hence the rates at which these changes occur (Rw)- 

 Ascertain their deviations. 



(4) If desired, identify and measure separately the exchanges 

 of water or volume in particular paths of gain or of disposal (p). 



(5) If desired, identify and measure separately other changes 

 in the organism (s, M, N) at diverse water increments and times; 

 changes of composition, structure, partition, rates, and frequencies 



