82 



TROPICAL MEDICINE AND HYGIENE 



very badly malarial place would show no parasites, i.e., if 

 examination were confined to adults the endemic index 

 would appear to be nil. 



Examination of the children who have, when born, 

 no immunity will show a higher index. In a very badly 

 malarial place some children in the first six months of 

 life will be found to be infected ; in the second six 

 months the proportion with parasites rapidly rises, and 

 in the second to fourth years the great majority, over 

 80 per cent., may show evidences on blood examination 

 of malarial infection. After the fifth year the propor- 

 tion showing such evidences rapidly diminishes, so that 



12 5 10 15 20 25 30 35 40 



FIG. 25.- 



-Negroes (native Africans). Hausa and Yomba Children, 



320; Hausa Adults, 100. Compiled from Official Report, Lagos, of W. H. 

 G. H. Best. 



in a very malarial place the majority may acquire im- 

 munity by the sixth year or even earlier, and practically 

 all before the tenth year. In a less malarial place the 

 proportion free from evidence of malaria in the first five 

 years of life will be higher, and in the second five years 

 lower, and in places where the amount of malaria is not 

 great, or where infection does not occur during part of 

 the year, as in temperate climates, a large proportion of 

 the population may never acquire immunity. 



A common method for determining the endemic index 



