Heat Elimination and Production. 



197 



35 per cent. During waking hours with the same subjects the average propor- 

 tion of the total heat required to vaporize the water from the lungs and skin is 

 21 per cent, noticeably lower than during sleep. The variations are from 19 to 

 26 per cent. 



In table 79 only those subjects are used with which we have experiments both 

 during sleep and during waking hours. As a matter of fact, we have experi- 

 ments with 38 other subjects during waking hours which give an average of 

 24 per cent instead of 21 with the 17 here reported. The total 55 subjects, 

 therefore, give an average of 23 per cent of the total heat as utilized to vaporize 

 the water from the lungs and skin in waking hours. 



Table 79. Proportion of total heat output used to vaporize water from the lungs 

 and skin during sleep and during waking hours in rest experiments. 



Taking these 17 subjects and assuming 8 hours of sleep during the night it 

 can be seen that the average per cent of heat required to vaporize the water from 

 the lungs and skin during 24 hours would be 23 per cent. 



In a lengthy series of experiments with fasting man it was found that 22 per 

 cent of the total heat eliminated was absorbed in vaporizing water from the 

 lungs and skin. An almost identical value was found in ten 24-hour experiments 

 with food, namely, 22.1 per cent. Accordingly, it would appear that the figures 

 here represent normal conditions and that we can state that during sleep man 

 normally utilizes 27 per cent of the total heat production in vaporizing water 

 from the lungs and skin, and during waking hours 21 per cent, the average of 

 the 24 hours of sleep and awake being not far from 23 per cent. 



During Muscular Work. 



Although the primary object of this report is to consider the metabolism of 

 normal man at rest and not during muscular work, it is advisable here to enter 

 into a discussion bearing upon the influence of muscular work upon the propor- 

 tion of the total heat required to vaporize the water from the lungs and skin, 

 inasmuch as in at least two earlier publications the discussion has been based 

 upon a somewhat erroneous foundation. 



It is important in this discussion to note that so far as the measurement of 

 total heat is concerned, it is a matter of indifference whether 1 gram of water is 

 vaporized from the surface of the man's body, from his ordinary clothing, from 



