IIo BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
although it might suffice for a few hours or save the life of a person who 
had been wholly without water. 
All devices for allaying the discomfort arising from the dryness of the 
mucous membrane, such as carrying bullets or pebbles in the mouth, 
chewing grass or a piece of rubber, are wholly futile in meeting the serious 
thirst problem. The relative humidity often falls to 5 per cent in the 
Southwestern deserts, and in a temperature of over 100° the evaporation 
from a vessel of water standing in the open may be as much as an inch 
a day. The amount thrown off by the skin is correspondingly great, and 
if the loss is not made good, thirst ensues, and ten hours’ lack of water 
may thicken the tongue so that speech is impossible. 
The Indian and the desert traveler often seek relief in the juices of 
plants when water fails. The fruits of some of the prickly-pears are slightly 
juicy, the stems of the same plant or the great trunks of the sahuaro 
contain much sap, but for the most part it is bitter, and while it would 
save life, in extremity, yetitis very unpleasant touse. The barrel-cactus, 
or bisnaga (Echinocactus) , however, contains withinits great spiny cylinders 
a fair substitute for good water. Togetatthiseasily onemust be armed 
with a stout knife or an ax with which to decapitate the plant, which is 
done by cutting away a section from the top. Lacking a suitable tool 
the thirsty traveler may burn the spines from the outside of the bisnaga 
by applying a lighted match and then crush the top with a heavy stone. 
This or other means is taken to remove a section 6 to 8 inches in thick- 
ness and expose the older parenchyma around the small central woody 
cylinder. Next a green stake is obtained from some shrub or tree that 
is free from bitter substances, and with this or with the ax the white 
tissue of the interior is pounded to a pulp and a cavity that would hold 
two gallons is formed. Squeezing the pulp between the hands into this 
cavity will give from 3 to 6 pints of a drinkable liquid that is far from 
unpleasant and is generally a few degrees cooler than the air (plate 62). 
Scouting Indians have long used the bisnaga, and a drink may be obtained 
in this manner by a skilled operator in 5 to 10 minutes. Some travelers 
are inclined to look with much disfavor on the liquid obtained in this 
manner, but it has been used without discomfort by members of expedi- 
tions from the Desert Laboratory. That it is often preferred by Indians 
to fair water is evinced by the fact that the Whipple Expedition found 
the Mohaves near the mouth of the Bill Williams River, in 1853, cooking 
ducks and other birds in the juice of these plants by means of heated © 
stones dropped into the cavity containing the pulp. 
The sap of the sahuaro (Cereus giganteus) and of other cacti contains 
bitter substances that make it impossible to be used to allay thirst by 
man, although it may be given to burros. A supply is usually obtained 
by felling the heavy trunk and elevating the ends a few inches above the 
ground, while the middle is allowed to sag lower over a bucket or vessel 
