HUMAN DISEASES 53 I 



out numerous experiments, mainly on the transmissibility of 

 human trypanosomes by animals. These have confirmed and 

 extended Dr. Duke's work, especially in regard to the part played 

 by animals as a reservoir for T. rhodesiense. In addition, the sleeping 

 sickness branch of the medical department has carried out exten- 

 sive surveys, and has established means of ensuring that very few 

 cases escape being reported. 



In Nigeria, since the establishment of the sleeping sickness 

 branch of the medical department, the wide distribution of the 

 disease has been demonstrated, and evidence has been brought 

 forward that it has increased in recent years. It is presumed that 

 much of the population, especially in the Southern Provinces, has 

 acquired some immunity to the local strains of trypanosomes, but 

 that the recent increase in motives or facilities for travel has led to 

 contacts with new strains which have often caused virulent epi- 

 demics. There have been examples of this in the middle belt, 

 where gold mining has stimulated migration, and also near Port 

 Harcourt in the south. Although T. gambiense is probably the only 

 causative organism, three types of the disease can be recognized, 

 which seem to depend on the degree of immunity which has been 

 attained by the people concerned. First there is a type showing 

 general weakness, but not a high death rate; the patients may suffer 

 for many years and their resistance to other diseases is lowered, 

 so that when death occurs it usually appears to result from other 

 causes. Secondly there is a toxic type in which death, when it 

 occurs, follows acute high temperature; and thirdly there is the 

 classic disease characterized by sleeping and mental trouble, symp- 

 toms which are absent in the first two types. It has been estimated 

 that there must be nearly a million cases in the Northern Provinces 

 of Nigeria alone, and although curative treatment has been suc- 

 cessful, it is recognized that treatment of this number every year 

 would be impossible. Hence, protective measures involving a 

 reduction of the man-fly contact by methods of communal clear- 

 ing, and movement and concentration of population, provide the 

 most hopeful line of attack. Research, centred at the Gadau 

 laboratory has been concerned chiefly with tsetse flies, and is out- 

 lined in Chapter X. Application was made in 1936 for a much 

 increased grant from the Colonial Development Fund to expand 



