uation of snowfall or rainfall that in a
moist region would be negligible, has conspicuous or even tragic
results. English engineers who examined the utilization of the Afghan
streams for irrigation reported that the natives had exploited their
water supply to the last drop; that irrigation converted the Kabul River
and the Heri-rud at certain seasons of the year into dry channels.[1128]
In the Turkoman steppes it has been observed that expanding tillage, by
the multiplication of irrigation canals, increased the loss of water by
evaporation, and hence diminished the supply. Facts like these reveal
the narrow margin between food and famine, which makes the uncertain
basis of life for the steppe agriculturist. Even slight desiccation
contracts the volume and shortens the course of interior drainage
streams; therefore it narrows the piedmont zone of vegetation and the
hem of tillage along the river banks. The previous frontier of field and
garden is marked by abandoned hamlets and sand-buried cities, like those
which border the dry beds of the shrunken Khotan rivers of the Tarim
basin.[1129] The steppe regions in the New World as well as the Old show
great numbers of these ruins. Barth found them in the northern Sahara,
dating from Roman days.[1130] They occur in such numbers in the Syrian
Desert, in the Sistan of Persia, in Baluchistan, the Gobi, Takla Makan
Desert, Turfan and the Lop Nor basin, that they indicate a marked but
irregular desiccation of central and western Asia during the historical
period.[1131]

[Sidenote: Scant diet of nomads.]

If a scant water supply places sedentary agriculture in arid lands upon
an insecure basis, it makes the nomad's sources of subsistence even more
precarious. It keeps him persistently on low rations, while the drought
that burns his pastures and dries up well and wadi brings him face to
face with famine. The daily food of the Bedouin is meal cooked in sour
camel's milk, to which bread and meat are added only when guests arrive.
His moderation in eating is so great that one meal of a European would
suffice for six Arabs.[1132] The daily food of the shepherd
agriculturists on the Kuen Lun margin of the Takla Makan Desert is bread
and milk; meat is indulged in only three or four times a month.[1133] The
Tartars, even in their days of widest conquest, showed the same habitual
frugality. "Their victuals are all things that may be eaten, for we saw
some of them eat lice." The flesh of