ANIMALS AND ARID CONDITIONS 373 
TABLE 1 
Comparison of Foodstuff Used, Oxygen Taken up, and Water Formed 
Metabolic level 10,000 keal 
Oogles Ohideiion EOS Nees 
Foodstuff used for Oxidation Water ae from 
kg of Food Formed De etee 
liter kg Disy Bute 
kg 
Fat 1.06 2130 Teng ots 
Starch 2.39 1980 TGS 17 
One further and rather striking fact is that fat yields almost 
twice as much oxidation water as starch. Seemingly fat is more 
advantageous to the water economy than starch. However, fat 
also yields more calories. This means that when the water yield 
is related to metabolic rate, the apparent advantage disappears. 
Let us make a simple calculation: A camel has a metabolic 
level of, say, 10,000 kcal, and if he uses exclusively fat or exclu- 
sively carbohydrate we can use the comparison presented in 
Ialole i, 
For a given metabolic level one finds that more water is formed 
if starch is metabolized, than would be formed by metabolism of 
fat. Also, the evaporation from the lungs, which is proportional 
to the oxygen consumption, is higher when fat is burned. Al- 
though water is formed in the oxidation of fat, the conclusions 
must be that: (a) incidentally to the necessary oxygen uptake 
water is evaporated from the lungs in an amount similar to that 
formed in the oxidation process, (4) the evaporation from the 
lungs is slightly higher when fat is metabolized, and (c) at a given 
metabolic level starch would yield more water than fat. The bio- 
logical truth is that fat 1s the most widespread form of energy 
storage in the animal kingdom, and in this sense the camel is no 
different from other animals. Fat gives more energy per weight 
unit than other foodstuffs, and the economy in carrying the re- 
serves as lightly as possible is indeed very useful, particularly to 
an animal that may be deprived of an adequate food supply for 
extended periods of time. The water economy of the camel, then, 
