WATER ITS RELATION TO METABOLISM 263 



tion difference between blood and tissues brought about by the 

 taking of water. Lessening the water intake may lessen the N 2 out- 

 put by hindering the digestion and absorption of proteid food. On 

 the other hand, an abnormal concentration of the blood and tissues 

 increases the breaking down of tissue proteid and the N 2 output. 



Of the total amount of water which the body takes up partly 

 in the form of drink, partly in food, and partly through the 

 oxidation of the hydrogen in the food, only a very small part is 

 removed in the faeces. The amount given out by the kidneys 

 varies with that taken in the food and drink, and according to 

 the amount transpired from the skin and lungs, and so is a very 

 variable quantity. The amount transpired by the skin and lungs 

 is less influenced by the uptake in the food than by muscular 

 activity and the temperature of the air. Atwater finds that in 

 work experiments two to three, or even four times more water is 

 given out than in rest. This more than compensates the increased 

 uptake in food and drink, and thus less water is excreted in the 

 urine. The sweat in hard work may carry away as much as 12 

 per cent, of the total nitrogen excreted (285 mg. N 2 per litre, 

 Zuntz and Schumberg). 



The work done in these experiments was driving a bicycle 

 wheel against friction. 



In the rest experiments the amount of water given off by the 

 skin and lungs was approximately the same during the day and 

 night, but was least in the second part of the night when the effect 

 of complete rest was greatest. In the work experiments the out- 

 put per hour was as follows : 



7 A.M.-l P.M. 



183-1 c.c. 



1-7 P.M. 

 188-2 c.c. 



7 P.M.-l A.M. 



57-4 c.c. 



1-7 A.M. 

 44'5 C.C. 



