



WATER AS A PRODUCT OF EXCRETION 351 



Oxygen , . .. . . ' . , -.- . . . . 0.824 



Nitrogen ., . .,....*> . ... 9-589 



Carbon dioxide . . - . ... * , . . . . . . 19.620 



The proportion of these gases was found by Morin to be subject to cer- 

 tain variations. For example, after the ingestion of a considerable 

 quantity of water or any other liquid, the proportion of oxygen was con- 

 siderably increased (from 0.824 to 1.024), and the carbon dioxide was 

 diminished more than one-half. The most important variations, how- 

 ever, were in connection with muscular exercise. After walking a long 

 distance, the exercise being taken both before and after eating, the quan- 

 tity of carbon dioxide was found to be double that contained in the urine 

 after repose. The proportion of oxygen was slightly diminished and 

 the nitrogen was somewhat increased ; but the variations of these gases 

 were insignificant. 



It is not probable that the kidneys are important as eliminators of 

 carbon dioxide, but the presence of this gas in the urine assists in the 

 solution of some of its saline constituents, notably the phosphates. 



Water as a Product of Excretion. It has been shown by indirect 

 observations that a large proportion of the hydrogen introduced as an 

 ingredient of food, about eighty-five per cent, is not accounted for by 

 the hydrogen of the excreta. Direct observations have shown, also, 

 that under certain conditions an excess of water over that introduced 

 with food and drink is discharged from the body. One of these con- 

 ditions is abstinence from food (Flint, 1878). The elimination of water 

 is much increased by muscular work (Pettenkofer and Voit, 1868 ; Flint, 

 1879). These facts point to the actual production of water in the body 

 by a union of oxygen with hydrogen. 



While it is not certain that water is constantly produced in the body, 

 there can be no doubt in regard to its formation under some conditions, 

 and the oxidation of hydrogen is important as one of the factors in the 

 production of animal heat. If a certain proportion of the water dis- 

 charged by the lungs, skin and kidneys is to be regarded as a product 

 of oxidation within the body, the relations which it bears to nutrition 

 probably are the same as those of some of the excretions, especially 

 carbon dioxide, and are subject to nearly the same laws. It has not 

 been shown, however, that water is produced constantly, like the sub- 

 stances commonly regarded as true excretions ; and it gives rise to no 

 direct toxic phenomena when retained in the system or when its produc- 

 tion is diminished pathologically. Water also has important physio- 

 logical uses, particularly as a solvent. Still, carbon dioxide, with which 

 water may be compared as regards its mode of production, is not in 

 itself poisonous, its retention in the blood simply interfering with the 



