126 Dr Stephens, The Prevention of Malaria. 



breeding grounds occur in the greatest profusion and in the huts 

 adult Anopheles are to be caught in myriads. 



But a more important side of this question still remains for 

 consideration, viz. where do we find infected A nopheles and by what 

 means do they become infected, for it is not so much the existence 

 or absence of Anopheles that is the vital question as whether or 

 no the mosquitoes contain sporozoites in their salivary glands ? 



We found that an examination of the salivary glands of 

 Anopheles caught in native huts always gave a certain proportion 

 of infected ones. This proportion was generally about 1 — 20 °/ '> 

 in some cases as high as 50 °/ an d in others again as low as 2 °/ - 



The highest percentages we unexpectedly found in those 

 places where Anopheles were at first sight scanty and where there 

 might be a complete absence of breeding grounds for at least 

 some months, whereas our lowest value 2 °/ was found in Lagos 

 island where there were innumerable breeding grounds ; and it 

 may be that the difference was dependent solely on the fact that 

 in the latter case the large number of insects always present was 

 sufficient to reduce the percentage of infected ones. 



All native huts examined by us contained infected Anopheles 

 in variable proportion. 



Source of infection of Anopheles. The source of this uni- 

 versal condition of infection was moreover made clear when 

 systematic blood examinations of the inmates of the huts were 

 made. For it appeared that we had in the huts a universal 

 condition of infection with malarial parasites and that this in- 

 fection was confined almost entirely to the youngest children, 

 especially those of 1 to 5 years old. It is not that these children 

 were suffering from attacks of " fever " in the ordinary acceptance 

 of the term, but that they, although to all intents and purposes 

 quite healthy, almost all contained parasites in their blood. Here 

 then was revealed a complete explanation of the mode of infection 

 of the Anopheles. Prof. Koch working at the same time in the 

 East Indies found an exactly parallel condition. 



Since these results were published some authors have at- 

 tempted to claim that this had been previously recognized. It is 

 not denied that the existence of malaria in children has long been 

 known, but it would appear that these authors have not realized 

 the actual condition that exists among native children which is, 

 that in children apparently perfectly healthy there exists an 

 almost universal condition of infection with malaria parasites ; 

 this, it will be recognized, is quite a different state of things to the 

 existence of cases of malaria among children : just as in small birds 

 in Africa there exists a very large infection (about 50 °/ ) °f Halteri- 

 dium, so in native children below a certain age, who are apparently 

 quite well, as many as 100 °/ may contain parasites in their blood. 



