poration and death from heat. The desert rodents avoid this dilemma by leading a 

 nocturnal life and staying underground during the daytime. Only under exceptional 

 circumstances if the body temperature should rise close to a fatal level, will they 

 use water for heat regulation. Under these circumstances the water will last for a 

 short time only. The actual time of survival found in the experimental work described 

 earlier in this paper was close to that which can be calculated from the surface- body 

 weight relationship. 



It is evident that the heat exchange between the environment and the body is 

 not as simple as assumed above. A very important factor is that the amount of heat 

 that reaches the body from the environment depends upon the surface insulation of 

 the body. In other words, the fur of an animal (or clothes in man) will cut down the 

 heat gain to an extent corresponding to its insulation value. This may seem para- 

 doxical, but it is nevertheless true that clothing in the desert reduces the heat load 

 and therefore is of advantage to the water economy. The value of clothing in man 

 has been clearly demonstrated under actual desert conditions by Molnar (Fig. 2). 

 However, water economy and greatest feeling of comfort do not necessarily coincide. 



-100 



-50 



Environmental Heat Gain Calories per hour 



+ 50 +100 +150 +200 +250 +300 



+350 



+400 



Figure 2. 

 This graph shows that tlie heat gain from a "hot" environment is much higher in the 

 "nude" man than in the "clothed" man- The graph is taken from V'oinar et al 

 { Arner.J.Hyg. 44, p. 417). The "nude" men wore shoes and light shorts, the "clothed" 

 men wore light clothing including shirts and trousers. The difference between "nude" 

 and "clothed" is particularly significant in the desert sunshine. 



185 



