Water. 467 



The wide variations in the amounts of drinking-water consumed by the 

 different subjects of these experiments have been discussed in detail in an 

 earlier section (see p. 3-18). The actual amounts consumed per 24 hours have 

 also been recorded in table 193. Similarly, the output of water of respiration 

 and perspiration has received special discussion in a preceding section, as has 

 also the amount of water in the urine. It remains, therefore, to consider in 

 detail the amount of water of oxidation of organic hydrogen and the loss of 

 preformed water. 



Water of oxidation of organic hydrogen. The water resulting from the 

 oxidation of organic hydrogen may be directly computed from the data for the 

 quantities of protein, fat, and glycogen katabolized and the analysis of the 

 urine. The percentages of hydrogen in these compounds are known (see p. 

 37), and the total quantity of organic hydrogen contained in them may be 

 computed. By deducting the organic hydrogen in the solid matter of the 

 urine, the total hydrogen oxidized is obtained. From these data in the different 

 experiments, the results for the water of oxidation of organic hydrogen as 

 recorded in table 229 may be obtained. The computation actually used in 

 obtaining these results was slightly different in form. In the calculations of 

 the quantities of protein, fat, carbohydrate, and water katabolized, according 

 to the method of simultaneous equations (see p. 38), the values found for 

 water represent only the preformed water involved in the katabolism, for the 

 organic hydrogen of the protein, fat, and glycogen had already been appor- 

 tioned among the various quantities of these three compounds. Deducting 

 the preformed water, as computed by the formulae, from the total water output, 

 gives the values for the water of oxidation of organic hydrogen. 



The water of oxidation of organic hydrogen is dependent upon the amounts 

 of protein, fat, and glycogen katabolized, and in nearly every case the amounts 

 decrease as the fast progresses. The largest amount in the fasting experiments 

 occurred on the second day of experiment No. 82, and the smallest amount on 

 the seventh day of experiment No. 75. The average water of oxidation for 

 all the fasting experiments is 209 grams, corresponding to the oxidation of 

 23.4 grams of organic hydrogen. The factors affecting the amounts of 

 protein, fat, and glycogen katabolized, therefore, obviously affect the amounts 

 of organic hydrogen oxidized. 



Each gram of organic hydrogen oxidized in food or body material is accom- 

 panied by a total liberation of about 70 calories of energy. 155 The comparison 

 of the organic hydrogen oxidized in these experiments with the total heat 

 output is deferred to the discussion of the heat elimination. 



Loss of preformed water. While the water of oxidation of organic hydrogen 

 is directly proportional to the amounts of hydrogen in the protein, fat, and 

 glycogen katabolized, and is, therefore, not properly to be considered in a water 



155 See the computations made by Magnus-Levy. Physiologie des Stoffwechsels 

 (1905), p. 424. Thus during fasting 32 grams of hydrogen corresponds to a total 

 heat output of not far from 2300 calories. 



