CORRELATIVES OF WATER CONTENT AND EXCHANGES 



267 



tion plays no special role in the time of appearance of the adult 

 response to water load. 



It seems possible to locate the water between the time it is put 

 into the pup's stomach and the time it is slowly lost. The stomach 

 is empty one hour after administration; the intestine is no fuller 

 at that time than in control individuals. Only slight volumes of 

 fluid are found in the peritoneal cavity. The blood plasma is di- 

 luted for at least 3 hours. I conclude that the water is absorbed 

 quickly, is retained throughout the body, and eliminated only very 

 slowly. This would mean that the pup in the first two weeks of 

 life is rather dependent upon receiving nutrients in proportions 



X 



I 



-o 











10 



zo 



30 80 700 



Days after Birth 



Fig. 136. Duration of the half -life of total water load in relation to age. Nine- 

 teen young dogs of 5 litters, and adults (N). Solid line represents the mean for all 

 litters, dotted lines represent 2 separate individuals of litter H. New data. 



and amounts determined by some agency outside itself ; regulations 

 of water and other substances develop before weaning is possible. 

 Similarly, water drinking is not demonstrable at birth. A very 

 young pup that takes milk from a bottle does not take water from 

 a bottle, indicating that the two ingesta are distinguished. The 

 newborn is not induced to take water by depriving it of water for 

 three hours, nor by administering a concentrated salt solution. 

 The first drinking of water as such I found at 15 days of age. So, 

 compensations by diuresis and by drinking appear at about the 

 same age. At first the drinking is slow; and the correspondence 

 between the water deficit and the amount taken voluntarily is not 

 close at 15 days of age, while at 35 days of age, hence before as well 

 as after weaning, the adult speed and accuracy have been acquired. 



