ANIMALS AND ARID CONDITIONS 37] 
Obtaining more water is not always simple. Large scale drilling 
for water has been practiced in the southwestern United States 
with effects on the water table that have been described as disas- 
trous. A similar decrease in the water table in some Old World 
arid areas would involve a much more precarious situation if wells 
in villages and oases were starting to dry up. Obviously, large 
scale irrigation cannot be started without careful consideration 
of long range effects, but when found possible, it is a most efficient 
way of handling the production problem. 
The other possibility is that of using the available water to 
better advantage. In the following I shall present some general 
considerations of this problem, and in order to illustrate principles 
I shall simplify matters as much as possible. 
In winter, the water content of the vegetation is high. At the 
same time the animals need relatively small amounts of water 
because the temperature is low and water is not used for heat 
regulation. Animals do not return frequently to the wells, and 
may therefore graze over large areas. They can utilize well the 
vegetation which is at its maximum productivity. The range of 
the animals is restricted by management and herding problems, 
and a nomadic (or semi-nomadic) management seems more 
advantageous because it will permit the utilization of areas far 
away from human settlements. 
The amount of water in the plants may be so high that at least 
the camel becomes completely independent of drinking water in 
the winter time. We have offered water to camels that had been 
without it for two months, and they would not drink. Subsequent 
examination of blood, tissues, stomach, etc., showed them nor- 
mally hydrated. In the summer the situation is different. The 
vegetation dries up, and at the same time the animals need water 
for heat regulation. 
In all deserts one finds some mammals, mostly small rodents, 
that seem completely independent of water. The American kan- 
garoo rats and the Old World jerboas, for example, do not drink 
water and can thrive indefinitely on only dry food. 
Even the driest seeds contain some absorbed water, but a 
larger quantity is formed by the oxidation of the food in the body. 
