The passage of the Kalahari was effected, not without considerable difficulty, in two months, the expedition reaching Lake Ngami on the 1st of August.  As they approached it, they came upon a considerable river.

“Whence does this come?” asked Livingstone.

“From a country full of rivers,” was the reply; “so many that no man can tell their number, and full of large trees.”

This was the first actual confirmation of the report of the Bakwains that the country beyond was not the large “sandy plateau” of geographers.  The prospect of a highway capable of being traversed by boats to an unexplored fertile region so filled the mind of Livingstone that, when he came to the lake, this discovery seemed of comparatively little importance.  To us, indeed, whose ideas of a lake are formed from Superior and Huron, the Ngami seems but an insignificant affair.  Its circumference may be seventy or a hundred miles, and its mean depth is but a few feet.  It lies two thousand feet above the level of the sea, and as much below the southern border of the Kalahari, which slopes gradually toward the interior.

Their desire to visit Sebituane, whose residence was considerably farther in the interior, was frustrated by the jealousy of Lechulatebe, a chief near the lake, and the expedition returned to the station at Kolobeng.  The attempt was renewed the following year.  Mrs. Livingstone, their three children, and Sechele accompanied him.  The lake was reached.  Lechulatebe, propitiated by the present of a valuable gun, agreed to furnish guides to Sebituane’s country; but the children and servants fell ill, and the attempt was for the time abandoned.

A third expedition was successful, although the whole party came near perishing for want of water, and their cattle, which had been bitten by the ‘Tsetse’, died.

This insect—­the ‘Glossina moritans’ of the naturalists—­deserves a special paragraph.  It is a brown insect about as large as our common house-fly, with three or four yellow bars across its hinder part.  A lively, buzzing, harmless-looking fellow is the tsetse.  Its bite produces a slight itching similar to that caused by the mosquito, and in the case of men and some species of animals no further ill effects follow.  But woe to the horse, the ox, and the dog, when once bitten by the tsetse.  No immediate harm appears; the animal is not startled as by the gad-fly; but in a few days the eyes and the nose begin to run; the jaws and navel swell; the animal grazes for a while as usual, but grows emaciated and weak, and dies, it may be, weeks or months after.  When dissected, the cellular tissue seems injected with air, the fat is green and oily, the muscles are flabby, the heart is so soft that the finger may be pushed through it.  The antelope and buffalo, the zebra and goat, are not affected by its bite; while to the ox, the horse, and the dog it is certain death.  The mule and donkey are not troubled by it, nor are sucking calves, while dogs, though fed upon milk, perish.  Such different effects produced upon animals whose nature is similar, constitute one of the most curious phenomena in natural history.