PROTOZOA AND HUMAN DISEASE 303 



the conditions of life easier. Both are brought 

 about in a large measure by the study of the parasitic 

 organisms that infect man and of the means whereby 

 disease is spread from man to man. Had it not 

 been for the researches of Laveran, who discovered 

 the malarial parasites in the blood, and the classical 

 work of Ross on the mosquito transmission of 

 malaria, full preventive measures could not have 

 been so easily devised. Button and Forde's dis- 

 covery of Trypanosoma gambiense, followed by the 

 inculpation of the tsetse fly, Glossina palpalis, gave a 

 basis both for preventive measures and for direct 

 treatment. The economic importance of these dis- 

 coveries is enormous, for such regions of the world 

 as West Africa and the Congo possess many of the 

 productions regarded as necessities of our present 

 civilization, together with a most fertile soil, capable 

 of great development. Yet, unless some means 

 of preventing sleeping sickness be devised, these 

 countries are destined to remain relatively unde- 

 veloped, the possession and often the grave of 

 nations among whom dwindling has progressed in 

 many cases. The Congo has claimed many victims 

 ere this, not only from trypanosomiasis, but from 

 spirochsetosis, or tick fever. It has only been by 

 patient and laborious work, that the mode whereby 

 the tick infects people and also passes on the Spiro- 

 chaetes to its own offspring, has become known. 

 Both spirochsetal tick fever and yellow fever cost 

 their early investigators their lives sacrifices for the 

 cause of suffering humanity. 

 The direct effects of the protozoal diseases of man, 



