372 THE FUTURE OF ARID LANDS 
On oxidation one gram of starch yields 0.6 gram of water and one 
gram of fat yields almost 1.1 grams of water. By exercising the 
greatest physiological economy with water expended for urine 
and feces and for evaporation (which cannot be completely 
avoided because the expired air is saturated with water vapor), 
those small rodents can just manage on the oxidation water, 
being independent of intake of free water. 
These small animals do not use water for heat regulation. They 
are nocturnal and remain in their underground burrows through- 
out the hottest part of the day. They are an ecological paradox, 
living in the desert without being exposed to the rigor of desert 
heat. 
The large animals cannot escape the desert heat by hiding 
underground. To avoid undue rise in the body temperature they 
evaporate water from the surface of the skin (sweating) or from 
the moist respiratory surfaces (panting). 
The oxidation water which goes a long way for the small 
rodents would not go far in the water economy of an animal 
using water for heat regulation. The amount of oxidation water 
formed in man is about one-quarter liter per day (on a metabolism 
of 2,000 keal) and is insignificant when sweating rates may be 
over I liter per hour or Io to 1¢ liters or more per day. 
Water and the Camel’s Hump 
This seems to be the place to discuss a widespread miscon- 
ception with respect to the role of oxidation water in the water 
balance of the camel. It has been said that since oxidation of fat 
yields more than its weight in water (1.07 grams of water per 
gram fat),-a camel that walks into the desert with a hump with 
40 kg fat actually carries a potential water supply of more than 
40 liters. This, of course, is true, and has led to the deceptive idea 
of “water from the hump.” What was forgotten is that oxygen is 
required to oxidize the fat. This involves ventilation of the lungs 
and loss of water in the expired air. The amount of evaporation 
from the lungs is of the same magnitude as the quantity of water 
formed. In very dry air it would exceed the oxidation water, and 
even in moderately dry air there will be no appreciable gain. 
