MILAN 



total heat loss and production between the soldiers and the Eskimos 

 were highly significant. The first law of thermodynamics allows us 

 to say that M ± D = H where M = metabolism, D = heat debt, and H = 

 the combined losses of heat through conduction, connection, radia- 

 tion, and evaporation (Carlson, 1954). We can assume that about 8% 

 of M is evaporative heat loss. In the 33 C bath, then, Eskimo and 

 soldier average metabolisms are 54.7 and 39.4 kcal/m /hr. By 

 subtracting 8% of these values we see that the Eskimos have 50 kcal/ 

 m /hr and the soldiers 36 kcal/m /hr available to lose to the 

 colder bath water without incurring a heat debt. They lost 86 and 

 66 kcal/m /hr, a difference of 20 kcal, and incurred body heat 

 debts at the same rates. The differences between heat produced and 

 total heat loss is then 36 kcal for the Eskimos and 30 kcal for the 

 soldiers. The Eskimos are characterized by a greater energy flux 

 through the system (a system which can be described as an iso- 

 thermal energy converter). In addition a greater mass of the Eskimo 

 peripheral tissue participates in this cooling. It is tempting to con- 

 clude that the Eskimos have smaller "cores" and larger "shells." 



Others (Carlson et al., 1958; Pugh et al., 1960; Cannon et al., 

 1960) have shown that subcutaneous fat is of considerable impor- 

 tance in reducing heat los^ in cold water. Hatfield et al. (1951) 

 have reported that the thermal insulation of 1 cm of fat is __^_, 

 kcal/cm^/sec. The experiments of Cannon et al. (1960) snowed 

 that fat men achieved a higher maximum tissue insulation in cold 



water than thin men. Carlson et al. (1958) have reported tissue 



o . / 2 , o , 



insulations that range between 0.10 C/kcal/m /hr and 0.40 C/ 



kcal/m /hr. Carlson's values are considerably higher than the tissue 



insulations reported here and are probably more nearly correct for 



steady state conditions above the critical temperature. 



368 



