526 SCIENCE IN AFRICA 



corpses, (2) the absence of registration of deaths, and (3) the lack 

 of staff for field work. 



The introduction of air travel has created the danger that the 

 disease may spread from endemic centres, especially in West 

 Africa, where a large proportion of the population seems to possess 

 some immunity owing to the prevalence of the disease, to East and 

 South Africa, and even to Asia, where the mosquito vectors are 

 abundant, and disastrous epidemics might occur among popula- 

 tions having no immunity. The spread of infected mosquitos can 

 be prevented by fumigation, but the principal danger comes from 

 passengers embarking during the incubation period of about six 

 days. The special commission on yellow fever of the Paris Inter- 

 national Office, under the Chairmanship of Colonel James, has 

 stressed this danger, and it has been discussed extensively at the 

 Pan-African Health Conferences in South Africa (League of 

 Nations 1933b and 1936). 



The disease is particularly prevalent in Liberia, which forms 

 a permanent reservoir for its spread to adjoining territories. Work 

 in Liberia by the Rockefeller officers shows that the majority of 

 children contract the disease, but among them the mortality rate 

 is only 5 per cent and complete immunity results. Among white 

 men in West Africa, however, who contract yellow fever as adults, 

 the mortality is more than 90 per cent. Hence there is a danger of 

 the disease being erroneously regarded as one chiefly affecting the 

 non-native population. 



The International Sanitary Convention for Aerial Navigation 

 of 1933 has been ratified by a considerable number of states. This 

 convention, to which all governments in Africa have agreed to 

 adhere, was prepared by the permanent committee of the Office 

 International d^ Hygiene Publique in Paris, and is designed especially 

 to prevent the risk of yellow fever spreading from its present 

 endemic centres. The fact that some governments are not prepared 

 to accept positive results obtained by the mouse protection test as 

 proof that yellow fever is present in the silent areas, adds emphasis 

 to the need for proving clinical cases. 



In towns and other localities where the disease has occurred, 

 continuous and, whenever possible, permanent measures are taken 

 for reducing the prevalence of the mosquito vector. These have 



