226 SCIENCE IN AFRICA 



trypanosomiasis are carried by wild animals; as a striking example, 

 the recent outbreak of rabies in East Africa may be cited. Owing 

 to lack of knowledge concerning carriers of the disease, the only 

 course possible was to slaughter all wild carnivora over wide areas. 



There is a particular aspect of animal ecology concerned with 

 the size and fluctuation of animal populations. Mr. Charles 

 Elton's work at the Bureau of Animal Population at Oxford has 

 shown the importance of this subject in the control of diseases and 

 pests which are directly or indirectly due to fluctuations in wild 

 animal numbers. Data collected (Elton 1931) show that many 

 animals undergo variation in numbers with a periodicity, usually 

 between three and twelve years, which is more or less constant. In 

 general, a particular species increases in numbers during a succes- 

 sion of favourable years and then there is a comparatively sudden 

 reduction, often due to an epizootic disease. Many diseases of wild 

 animals are transmissible to domestic animals and to man, and 

 sometimes the wild animals, although unaffected themselves, may 

 serve as carriers of disease. Therefore the understanding of animal 

 periodicity may aid the control of epidemics among human beings 

 as well as epizootics among domestic animals. Little enough is yet 

 known of this subject even in Europe or America, while in Africa 

 it has scarcely been touched. 



A related problem is the introduction of diseases into regions 

 where they were previously unknown. For instance, rinderpest, 

 which is enzootic in Asia, appeared in Egypt in 1844 and 1865, in 

 Abyssinia in 1890, and by 1900 had spread along the Nile valley 

 through East Africa to the southern part of the continent and also to 

 West Africa. To-day there is a constant fear of its spreading through- 

 out the Union. During the passage of the disease through these 

 areas and subsequently at intervals, herds of wild game, especially 

 buffaloes, became infected, spread the disease among stock and 

 died in large numbers. The occurrence of this disease in epizootic 

 form is probably connected with the fluctuation of game popula- 

 tions, and when these are understood there should be a means of 

 forecasting epizootics. A similar example, though of a disease 

 affecting human beings as well as other mammals, is that of the 

 introduction of plague to South Africa, and its spread through the 

 agency of indigenous rodents. This subject, which has involved 



