In the old slavery days it was found that the negroes from the Congo region in the course of the voyage or after they were landed sometimes were affected with a peculiar disease.

They were lethargic, took little notice of their surroundings, slept easily and finally passed into a condition of somnolence in which they took no food and gradually died.
There was no extension of the disease and it was attributed to extreme homesickness and depression.

A similar disease has been known for more than one hundred years on the west coast of Africa, and attracted a good deal of interest and curiosity on account of the peculiar lethargy which it produced and from which it has received the name of "sleeping sickness." Although apparently infectious in its native haunts, it lost the power of spreading from man upon removal to regions where it did not prevail.

At first confined to a very small region on the Niger river, it gradually extended with the development of trade routes and the general increase of communications which trade brings, until it prevails in the entire Congo basin, in the British and German possessions in East Africa, and is extending north and south of these regions.

The cause of the disease and its mode of conveyance was discovered in 1903.