lO SCIENCE IN AFRICA 



as destroyers of crops stock and even man himself, and in pro- 

 viding reservoirs for diseases such as rinderpest, trypanosomiasis 

 and east coast fever, which may endanger domestic animals. It 

 appears that the western parts of Africa have never supported wild 

 game in numbers comparable with the east, but for a century or 

 more this difference has been accentuated by the extensive use of 

 firearms in West Africa. In general throughout Africa there has 

 been a pronounced change in the last fifty years, in that the num- 

 ber of wild beasts has been reduced to a striking degree, the extreme 

 being reached in those parts where anti-game campaigns are being 

 waged with a view to ridding the country of tsetse flies, as in 

 Southern Rhodesia. But there are certain exceptional areas, 

 mainly the game reserves, where the African now lives under the 

 restraint of game ordinances, so that the number of animals sur- 

 rounding his farms and stock ranches is greater now than ever 

 before. On the whole it appears that the development of game 

 organizations has led the African to rely for the protection of his 

 possessions more on the local game scout armed with an elephant 

 rifle than on his own prowess. 



The water environment, sea, lakes, and rivers, as a source of 

 food for man, is likewise undergoing change. Sometimes the stocks 

 offish have been reduced by the introduction of European methods 

 of fishing, or by commercial exploitation; in certain cases exotic 

 fish have been introduced to African lakes and streams; but on 

 the whole the fishery resources of the continent present a con- 

 siderable undeveloped opportunity for human activity. 



In the subject of cultivation we start with conditions in which 

 man has become closely adapted to the environment of climate 

 soil and vegetation, having evolved systems of shifting cultivation. 

 Two kinds can be distinguished; one in which the people live 

 permanently in the same place and cultivate surrounding plots in 

 rotation, and the other in which the village sites are changed at 

 frequent intervals. The former is characteristic of comparatively 

 dense populations, and the latter of forest areas where there is no 

 limit to the amount of land. The really important factor is the 

 proportion of resting years to cropping years necessary for the soil 

 to regain its original fertility, a proportion which varies through- 

 out the continent from about 1/3 up to 1/ infinity. The proportion 



