WATER RELATIONS OF MAN 95 



pendent upon the load a half-hour previously (that the response 

 occurred with a lag such as occurs at the initiation of diuresis). 

 Then the return in diuresis might easily overshoot the volume 

 ingested; an initial water excess would give rise to an ultimate 

 water deficit. Hence the rate of diminution (deceleration) of 

 water output might conceivably be an optimal process. Were the 

 deceleration faster, overshooting might frequently occur. Were 

 the deceleration slower, the restitution of water balance would 

 appear to be less sensitive to changes, and the tail-end of any diure- 

 sis would be much prolonged. Unfortunately no quantitative 

 expression can be given to this virtual optimum, the absence of 

 other factors (as always in problems of optima) being only a sup- 

 position. But I wish to emphasize that this deceleration is of 

 consequence to the organism. 



Without presenting further data for man, I conclude that the 

 rates of water loss are very similar during stationary rates of 

 water intake and during recovery (beyond the first 1.0 hour) from 

 single water administrations. The only significant diversities are 

 in loads less than + 1% of Bq; in them unidentified factors exert 

 their influences. But in both repeated and single administrations, 

 the constancy of rate of output with all loads above + 1% of Bo in 

 man is in marked contrast to the dog ; it implies a maximal capac- 

 ity for elimination and an inconstant velocity quotient. It may be 

 noted, however, that some human individuals have exhibited 

 higher rates of elimination than any shown in figures 52 or 55 {e.g., 

 Haldane and Priestley, '16) ; these individuals appear to augment 

 their losses as the loads increase above -j- 1 or even + 2% of Bq. 

 In any case the rates of water excretion are proportional to water 

 load over a narrower range in man than in dog. 



<^ 29. Water deficits 



Water deficits are studied by the following procedures. The 

 subjects deprive themselves of all liquids and of foods containing 

 large proportions of water, but maintain adequate food intakes. 

 The diet is not strictly constant in some cases ; in others it consists 

 of uniform amounts of butter, sucrose, and casein. Usual activi- 

 ties of the subject are continued. After measured losses of weight, 

 water is offered either in ad libitum amounts or in uniform 

 amounts at ad libitum times. The quantities drunk are ascer- 

 tained, and they represent the gains of water (fig. 56). 



