A set of 50 photographs and associated handwritten descriptive notes, acquired from the Imperial Russian Geographical Society in St. Petersburg. The complete notes, "1904 View of Great Tibet", are available at: http://collections.lib.uwm.edu/u?/tibet,94
"They are shrewd and enterprising traders, and able to hold their own even with the Chinese, to whom they sell large quantities of lambskins, wool, yak-hides, musk, furs (principally lynx and fox skins), rhubarb and deer-horns (lu jung). […] They have but very few camels, as they are essentially mountaineers, using principally yak or dzo2 (a cross between a domestic cow and a yak) as beasts of burden; moreover, the hair of these animals, which on the belly and legs is nearly a foot long, supplies the material of which they make their tents. Both the Tibetans and the Mongols often use the yak as a saddle animal. A wooden ring is passed through the cartilage of the nose, and a string is attached to it by which the animal is guided and fastened to the ground at night. (p. 75).
Rockhill, W.W. (1891). The land of lamas. New York: Century.
Google Books at: http://books.google.com/books?id=tNkMAAAAIAAJ&pg=PA1&dq