14 SCIENCE IN AFRICA 



throughout West Africa, and in parts of East Africa, is supposed to 

 have been introduced in comparatively recent years. Certainly its 

 distribution around the Guinea Gulf is now extending inland from 

 a number of foci near the coast. 



The influence of these factors on the food supply is one of the 

 most obvious ways in which they may affect human welfare. The 

 social significance of seasonal changes in the quantity of food 

 available has recently been studied by anthropologists as part of 

 the analyses of the native agricultural practice and economic 

 organization. Variation in quality of food is also important, since 

 different items in the dietary become available at difTerent seasons, 

 often for only very short periods. These variations are particularly 

 significant in the case of African peoples whose staple diet is gener- 

 ally so monotonous that the curtailment of any of the subsidiary 

 foods, small though the proportion of the diet that they represent 

 may be, may result in a complete lack of animal proteins or other 

 essentials, and so give rise to malnutrition and disease. Therefore, 

 on the variation of food supply depends to some extent the African's 

 resistance to disease, and hence the relation to the last of our 

 environmental categories. 



The internal environment of the human organism above all 

 others is altered by its biological content, and is capable of adap- 

 tation thereto, as shown particularly well by immunity or partial 

 immunity to diseases. Some of the changes involved may be illus- 

 trated by reference to three important diseases: malaria, yellow 

 fever, and sleeping sickness. Nearly every African is infected 

 with malaria before he is three years old, and subsequently develops 

 at least a partial immunity, because his body at that age is capable 

 of much greater adaptation than later on. In many parts of Africa 

 measures are now being taken to stamp out malaria, particularly 

 in townships, and a section of medical opinion favours the exten- 

 sion of these measures into rural areas wherever possible. Such 

 action would probably reduce the high infant mortality of many 

 parts of Africa. But the adult native, who had not become inocu- 

 lated in childhood, would be certain to meet the disease at a later 

 stage in life when his adaptability is not so great. 



Yellow fever also is often contracted by Africans at an early age; 

 the patient either dies or attains immunity for life. Recent work 



