WATER RELATIONS OF MAN" 105 



Another situation in which water exchanges were measured is 

 found when a man walks in hot and in cool environments (Dill et 

 al., '33). In hot weather the exchanges of water (by evaporation 

 and by drinking) are much larger. The progressive decrease of 

 water content during them, though drinking is allowed, is also large 

 as compared with the dog's in fig. 48. In man drinking is never 

 sufficient to make up for the loss of weight that occurs in the same 

 period of time. Hence no stationary state of water load is reached 

 while the man walked in the desert, yet it is quickly reached in the 

 dog. 



Variations, then, in the water loads and water exchanges of 

 man are of two sorts, in rhythms and without apparent rhythms. 

 Use of long periods of time in measuring exchanges, and of aver- 

 age data concerning them, tend to hide both sorts. As with many 

 other activities, what is usual at one time may be incongruous at 

 another. The kinetic equilibration of water content is itself a 

 mean in a set of relations, about which distinguishable modifica- 

 tions oscillate. 



<^ 33. Characterizations and tests 



Given the usual situation that a whole equilibration diagram for 

 all times elapsed cannot be worked out on each man to be studied, 

 what particular tests will yield crucial information? And even 

 when a diagram has been worked out, what points in it are likely 

 to characterize the individual or the species ? In many physiologi- 

 cal phenomena, empirical tests of this sort have been selected by 

 convenience, usage, and experience, to differentiate experimental 

 and pathological states. 



(1) Often, for instance, an individual is either too young or 

 too paralyzed to drink water from a cup, but can swallow water 

 when it is put into the mouth or can receive it by stomach tube. 

 How shall I ascertain whether he is deficient in water content? 

 One test is to administer 1 or 2% of Bo of water and see whether 

 the rate of urinary output more than doubles within 1.5 hours ; or, 

 how much of the water appears as urine within 4 hours. For most 

 individuals the position of their water contents at hour, relative 

 to the content at presumptive balance 4 hours later, may thus be 

 ascertained. 



A test of a similar sort has been in clinical use for many years, 

 Volhard's "Wasserversuch." In its usual form a subject is given 



