102 PHYSIOLOGICAL REGULATIONS 



appropriate ; sometimes by impulse and sometimes by experience. 

 In desert journeys, they travel at night and in shade, minimizing 

 the creation of water deficits through evaporative loss. They are 

 said to become restless when in water shortage, just as infants 

 become restless. Concerning water excesses where choices of envi- 

 ronment were permitted, on the other hand, not even such crude 

 facts are known. 



§ 31. Comparison with dog 



The data interrelating the compensatory processes in man (fig. 

 61) are obtained under conditions that at present appear to be the 

 same as those prevailing in dog (fig. 13). What similarities and 

 differences occur among the results? These are first and pro- 

 visional comparisons; ones made below (chapter IX) will concern 

 several species more exhaustively. Heretofore results might have 

 been generalized from one species; now distinctions may also be 

 found. 



Initial states are studied under which increments of water con- 

 tent are being dispelled after excess of water has been introduced 

 by mouth or deficit created by privation. The differences are : (a) 

 at any given excess of water (computed as % of Bo) the dog ex- 

 cretes water (per unit of Bq) about twice as fast as the man. Maxi- 

 mal rates of elimination by the dog far surpass those by man. If 

 some other factor than body weight were used, the same conclusion 

 would hold, for the factor cancels out by considering AW along 

 with its correlative SW/At; in other words, the net velocity quo- 

 tients (1/At) are greater in dog than in man. (b) In any deficit 

 of water the dog ingested water much faster than man. The dog 

 more than made up the whole deficit in 0.1 hour ; the man required 

 some hours to do so. (c) In deficits the sparing of urinary loss is 

 greater in dog than in man. This is related to the fact that dog's 

 urine may carry much more solute, be more highly concentrated. 

 Hence all modifications of water exchange are smaller in man than 

 in dog. (d) All responses are slower, in initiation, in accelera- 

 tion, in half -life, and in completion, in man than in dog. 



These differences are far greater than the differences among 

 individuals (standard deviations) for one species or the other. 



Among uniformities between man and dog are found: (n) In 

 the equilibration diagram the rates of loss are represented by a 

 curve having three limbs. The middle steep limb shows rates of 



