200 Metabolism of Healthy Man. 



the heat of conduction and radiation, and heat of vaporization of water. Thus, 

 with the subject J. C. W., with severe muscular work, the total heat elimination 

 was 514? calories, of which 1957 calories were required to vaporize water or 38 

 per cent of the total. During very severe muscular work, the heat production 

 increased to 9314 calories and the heat used to vaporize water was increased to 

 4325 calories so that of the increase of 4167 calories in the total heat produc- 

 tion, considerably over 50 per cent or 2368 calories was required to vaporize 

 water. Similarly, with the subject A. L. L., with severe muscular work the 

 heat elimination was 4727 calories, of which 2078 calories were required to 

 vaporize water. During the very severe muscular work, the total heat elimina- 

 tion increased to 7137 calories, of which 3480 calories Avere required to vaporize 

 water; thus, in the increase from severe to the very severe muscular work the 

 total heat elimination increased 2410 calories while the heat required to vaporize 

 water increased 1402 calories or 58.2 per cent of the total heat elimination. It 

 is obvious, therefore, that from 55 to 60 per cent of the increase in heat elimi- 

 nation resulting from increased muscular work leaves the body as latent heat 

 of water vaporized from the lungs and skin. The important role that perspira- 

 tion plays in the heat regulation is strikingly shown by experiments of this type. 



ENERGY GIVEN OFF BY THE BODY IN DIFFERENT WAYS. 



The preceding discussion with regard to the proportion of heat required to 

 vaporize water from the lungs and skin during different conditions of mus- 

 cular activity leads naturally to a discussion of the energy given off from the 

 body in different ways. As has been pointed out previously, the paths for the 

 excretion of heat during rest are bv radiation and conduction and in the water 

 vaporized from the lungs and skin, only a small amount being excreted in the 

 form of urine and feces. During muscular work a fourth path, namely, the 

 heat equivalent of external muscular work performed, is utilized. 



As has already been pointed out, in the earlier publications an erroneous 

 calculation was made in the amount of water vaporized, thus introducing an 

 error into the calculation of the heat of vaporization of water. The results, 

 therefore, are repeated here and given in table 81 for two reasons; first, to show 

 the relative proportions of energy excreted in the various ways and, second, to 

 give a permanent record of the correct values for experiments of this type. 

 Furthermore, the experiments given in this table, both for rest and for work, 

 are sufficient in number to show the characteristic differences in the apportion- 

 ment of the total energy to the different paths during rest and during work. 

 The table is copied exactly as given in the previous publication save that the 

 correct calculations are made, basing the proportion of the water vaporized from 

 the lungs and skin upon the total water of respiration and perspiration, rather 

 than upon the water-vapor leaving the chamber. 



From the average of the rest experiments, it is seen that 77.3 per cent of the 

 total heat eliminated leaves the body by radiation and conduction, 0.7 per cent 



