IMMUNITY 235 



they acquire immunity ; whereas the whites continue to suffer 

 if anything more and more severely as they become weakened- 

 The latter cannot acquire permanent immunity. They cannot 

 rear families, and a white settlement in African swamps or forests 

 would soon become as extinct as the British colony in Darien. 

 The following from Miss Mary Kingsley is very much to the 

 point : 



393. " Yet remember, before you elect to cast your lot with the 

 West Coasters, that 85 per cent, of them die of fever, or return 

 home with their health permanently wrecked. Also remember 

 that there is no getting acclimatized to the Coast. There are, it 

 is true, a few men out there, who, although they have been resident 

 in West Africa for years, have never had fever, but you 'can count 

 them on the fingers of one hand. There is another class who 

 have been out twelve months at a time, and have not had a touch 

 of fever ; these you want the fingers of your two hands to count, 

 but no more. By far the largest class is the third, which is made 

 up of those who have had a slight dose of fever once a fortnight, 

 and some day, apparently for no extra reason, get a heavy dose, 

 and die of it. A very considerable class is the fourth those who 

 die within a month or a fortnight of going ashore. 



" The fate of a man depends solely on his power of resisting 

 the so-called malaria, not in his system becoming immuned to it. 

 The first class of men I have cited have some unknown element in 

 their constitutions that renders them immune. With the second 

 class the power of resistance is great, and can be renewed from time 

 to time by a spell home in a European climate. In the third 

 class the state is that of cumulative poisoning ; in the fourth of 

 acute poisoning." x 



394. Now since acquired immunity arises most rapidly in acute 

 diseases in which virulent toxins are most abundantly and quickly 

 produced, since it arises slowly when toxins are less abundant or 

 more gradually developed, and since it never arises when the 

 evidence indicates that poisoning by toxins plays a minor part or 

 no part at all in the disease, it is clear that acquired immunity is 

 due directly to the presence of the toxins, not to the presence of 

 the microbes. This hypothesis is confirmed by the fact just 

 mentioned, that in acute diseases the phagocytes are able to 

 approach and destroy the microbes as soon as the symptoms ot 

 acute poisoning are mitigated, whereas in the more chronic 

 maladies, though from the first undeterred by toxins, they are 



1 Travels in West Africa, pp. 526-7. Macmillan & Co. 



