CORRELATIVES OF WATER CONTENT AND EXCHANGES 



269 



When excessive water is ingested by the human infant the pro- 

 portion of it returned by renal diuresis is small in the first months 

 (Ohlmann, '20; Lasch, '22). It is not certain that the transforma- 

 tion of compensatory adjustment is as sudden as in the dog. Only 

 after 6 months of age in man is the return as prompt and complete 

 as in adults. There is some evidence that at 5 to 10 years of age 

 the urine excreted within 3 hours markedly exceeds the water given, 

 which is not the case in adults (fig. 49). In these measurements, 

 a number of unrecognized differences other than age may exist; 

 also, differences such as size of ingestion, or promptness and ease 

 of micturition, may be legitimately included in a single variable. 



In frogs {Rana esculenta), where metamorphosis and respir- 

 atory modifications are proceeding apace (table 30), age is less 



TABLE 30 



Bates of water turnover at diverse sizes and ages in Eana temporaria at 18° to 22° C. 

 Anus and mouth were ligated for 3 to 5 hours. Data of Bey ( 'S7, p. 1132) 



* Mouth not ligated. 



correlated with body size ; no single rule is apparent in the rates of 

 water turnover recorded. Physiological metamorphoses inevita- 

 bly accompany aging in many or all species. 



Based on body weight, the turnovers decrease with age in dog, 

 man, and rat, but not in bovine and frog. In water increments the 

 rates of intake or output, the time relations of exchanges, and the 

 velocity quotients also show diverse modifications at different ages. 

 This fact may adequately prevent anyone from viewing regulations 

 as fixed properties of unchanging organisms. 



(2) Among species. Correlations with body weight furnish a 

 wide opportunity for comparisons among species. Data upon 

 rates of water exchange are available in mammals of very diverse 

 sizes for (a) total water intake (or turnover) in water balance and 

 (b) maximal water intake after hypophysial injuries (fig. 138) ; (c) 



