During the first part of the journey each of the boys watched the camel of the other, in order to understand the motions of his limbs and to observe the peculiarities of his feet. The Doctor explained that the foot of the camel is wonderfully adapted to travelling over the sands of the desert. It is divided into two lobes, and each lobe is armed with a stout claw, like the point of the ox's hoof. The foot is like a great sponge, and when placed on the ground it spreads out very wide, but is immediately contracted when raised. It thus presents a broad surface to the sand or mud, and where the ground is steep and slippery it clings like the foot of a fly on a window-pane. The strong claw assists its adhesion, and consequently the camel can climb the side of a mountain which is impassable to a well-shod horse. [Illustration: FOOT AND STOMACH OF THE CAMEL. 1, Fore-foot; 2, sole; 3, hind-foot, side; 4, structure of the stomach.] His nostrils are formed so that he can close them at will to keep out the drifting sand, and his stomach is so contrived that it will hold a supply of water sufficient for six or eight days. There are numerous cells or cups in the animal's stomach, and when he has plenty of time for drinking he fills all these cells, and thus accumulates a store for future use. His scent is very keen, and he can discover water at a great distance, and will sometimes break his halter and rush in search of a pool or spring of whose existence his master is not aware. He can get along with a very small quantity of food, and can, moreover, lay in a supply for hard times. [Illustration: HEAD OF A CAMEL.] When he is not at work, and has good pasturage, the camel becomes fat, and his hump is especially round and full--it is a mass of fat; and when he is overworked and poorly fed, as he generally is in the desert, the fat goes away from the hump to nourish the rest of the body. This is particularly noticeable of the camels in Asia Minor, where they are in very active use till they get worn to skeletons, and are then turned out to rest and recover their fat. [Illustration: THE DROMEDARY REGIMENT OF NAPOLEON I.] Camels are not unfrequently used by the Egyptian Government for military purposes, not only for carrying provisions and other munitions of war, but for mounting troops in regions where it is necessary to make long marches over the desert. Napoleon Bonaparte, during his expedition to Egypt in 1798, organized a regiment of this kind, and found it of great service. Officers and men were mounted on camels or dromedaries, and on one occasion they made a march of ninety miles without halting for food or rest. Napoleon was greatly pleased at the success of his scheme, as it enabled him to move his men more rapidly than by any other means.