Page:Popular Science Monthly Volume 69.djvu/417

Rh and Chamberland filters indicates that we have to do in this disease with organisms too minute to be seen. Ultra-microscopic protozoa are not the only ones which will do this, for small amœbas may, under pressure, be forced through some of these niters, while in a few organisms, notably the flagellates, there are some phases in the life history when the individuals become so small that they are no longer discernible with the highest powers of the microscope. This is the case in certain of the trypanosomes and spirochetes, which are now known to cause some of the most malignant of human diseases.

In this country, and indeed in temperate zones generally, there is no dread of trypanosomes, and 'sleeping sickness' is more often the subject of thoughtless jest than of intelligent consideration. In England, where African interests are more keenly followed, a deep interest is taken in this matter, and the Liverpool School of Tropical Medicine deals largely with trypanosomiasis. In his presidential address before the British Association for the Advancement of Science, meeting in South Africa last summer, Colonel Bruce said:

Trypanosomiasis in man, the 'sleeping sickness,' which occurs on the west coast of Africa, particularly in the basin of the Congo, has within the last few years spread eastward into Uganda, has already swept off some hundreds of thousands of victims, is spreading down the Nile, has spread all round the shores of Lake Victoria and is still spreading southward round lakes Albert and Albert Edward, and now threatens the Transvaal and Zululand.

Many different species of trypanosomes are known, and the normal habitat is the blood. No form of vertebrate is exempt, the blood of fish and amphibia, reptiles, birds and mammals forming suitable culture media for their growth and reproduction. In some stages of their life history they apparently become intra-cellular parasites, lose their flagella and membranes and assume the gregarine-like form. In man they may be either comparatively harmless flagellates, swimming about in the blood plasm, or, by bursting of the capillaries, they may penetrate the membranes of the brain and spinal cord and give rise to the invariably fatal disease of man—'sleeping sickness.' The presence of Trypanosoma gambiense in the human blood gives rise to the 'trypanosome fever' of Africa, not much worse apparently than is malaria in this country, but when the parasites enter the nervous system and congregate in the cerebro-spinal fluid, or in the ventricles of the brain, the result is invariably fatal. The result of this nerve-invasion is the appearance of various nervous symptoms like apathy, lassitude, trembling, and, finally, somnolence, increasing to a phase of intense coma and