PATHOGENIC PROTOZOA 413 



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 amcebas may, under 

 pressure, be forced through some of these niters, while in a few organ- 

 isms, notably the flagellates, there are some phases in the life history 

 when the individuals become so small that they are no longer dis- 

 cernible 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. 



Trypanosomiasis and the 'Sleeping Sickness' 



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 Eng- 

 land, 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. 2 



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 pene- 

 trate the membranes of the brain and spinal cord and give rise to the in- 

 variably fatal disease of man — ' sleeping sickness.' The presence of Try- 

 panosoma 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 congre- 

 gate 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 ap- 

 pearance of various nervous symptoms like apathy, lassitude, trembling, 

 and, finally, somnolence, increasing to a phase of intense coma and 



2 Science, XXII., p. 298, 1905. 



