254 PHYSIOLOGICAL REGULATIONS 



{!) showing that another type of water increment has other water 

 distributions, as indeed has been partially established in dog, or 

 (2) using some other measure of volume or concentration than 

 those underlying the present conclusion. 



Among metabolic rates, alimentary secretions are qualitatively 

 modified alike in dog and in man, but quantitatively the data are 

 not accurately enough controlled for comparisons. Clearances are 

 augmented on different scales in dog, man, and rabbit. Rates of 

 excretion appear to vary similarly with it AW in dog and in man. 



I think it would be possible to distinguish a herd of ten indi- 

 viduals of some one species from any of the other five species of 

 mammals discussed, by studying their physiological states in water 

 excess or in water deficit. With the inclusion of still more species, 

 probably the single distinctions would become blurred by inter- 

 mediate conditions of composition and metabolism, but the combi- 

 nations would not. What measurements would be chosen first, in 

 order to differentiate among species? Present evidence would 

 point to : urinary rate and drinking rate, dilution of dry residue of 

 plasma, urea clearance through kidneys, and volume of distribu- 

 tion of vital red. Of course, preference for these measurements 

 and criteria depends partly on the fact that they have already been 

 used ; better methods are probably awaiting discovery. Outside of 

 vertebrates there are few criteria for distinguishing species by 

 their responses to water increments, for modifications of rates of 

 oxygen consumption in positive water loads have alone been tested 

 to the point where marked correlation is known to exist. 



In my opinion not all, perhaps none, of the modifications accom- 

 panying water loads are ' ' accidents. ' ' Some or all are parts of the 

 process of recovery, spring boards by which equilibration takes off. 

 But, neither my predecessors nor I am able to decide which are the 

 ones that contribute toward recovery, and which not. Recovery of 

 water content has not been shown to be so rapid or so complete 

 without them. 



