374 THE FUTURE OF ARID LANDS 
is not located in the fat of the hump. Strict economy in water 
expenditure is the all important factor. 
Water Economy of the Camel 
It was mentioned before that the sweating rates of man in the 
hot desert may be as high as 16 liters per day or more. Compared 
with this quantity, the water lost in urine is quite insignificant. 
The minimum urine output in man is about 300 ml per day, and 
if the kidney were more efficient and could produce twice as con- 
centrated urine, it would be possible to save 150 ml of water, or 
one per cent of the amount evaporated. While such an efficient 
kidney is essential to the kangaroo rat, the relative saving is unim- 
portant in a large animal that uses water for heat regulation. The 
quantity of water used for evaporation may be tremendous, and 
if some economy could be accomplished in this amount it would 
be of great significance. 
When the temperature of the environment rises above that of 
the animal (more precisely, that of the skin surface) heat will be 
conducted to the animal from the hot surroundings by conduc- 
tion from the air and by radiation from the sun and the hot 
ground. Body temperature can be kept from rising only by evapo- 
ration of water. 
It is a consequence of the simplest physical laws that less heat 
will reach the animal surface if there is an insulating layer be- 
tween the heat source and the body. There is a great deal of 
physiological truth in the old saying that the Arab wears so 
many garments to exclude the desert heat. The woolly coat of 
the camel has a similar function in the summer. In our recent 
experimentation we showed that the camel’s fur was an efficient 
factor in reducing water loss in the summer. Of course, the fur is 
also an efficient insulation against loss of body heat in the winter. 
Another and major factor in the water economy of the camel 
is the variation in his body temperature. In the summer a camel 
may have a morning temperature of 34° and an afternoon maxi- 
mum of 40.6° to 40.7°. Man, when exposed to a hot environment, 
will, by evaporation of water, maintain a practically constant 
body temperature of about 37°. The variability of the camel’s 
