234 HUMAN DISEASES 



peril in deadly peril, if exposed to reinfection under unfortunate 

 conditions. The fact that he has experienced the disease is evi- 

 dence that he is susceptible to it, not that he has acquired increased 

 resisting power. 



391. Between such diseases as smallpox which run a short, 

 sharp, definite course during which acute poisoning occurs, and 

 such maladies as tuberculosis which are unmarked by acute 

 poisoning, and run a course of quite uncertain but always relatively 

 prolonged duration, lie such complaints as enteric fever and 

 syphilis. The onset, course, and recovery from enteric fever, 

 unlike that from smallpox, is comparatively slow, but not so slow 

 as in the case of tuberculosis ; nevertheless, there are very distinct 

 symptoms of poisoning, and the duration of the disease is pretty 

 definite. In syphilis, the onset of the disease is even more delayed, 

 the symptoms of systemic poisoning as indicated by fever and a 

 feeling of illness are, as a rule, hardly observable, 1 and the microbes 

 may persist in the system for two or more years. Nevertheless, the 

 disease ultimately confers an immunity which is usually permanent. 



392. Malaria occupies a curious position. Its toxins are 

 abundant and virulent, and the reaction to them is sharp and 

 rapid. The individual develops high fever and other symptoms 

 of poisoning ; but presently the symptoms abate ; apparently the 

 microbes cease to produce toxins ; the individual appears to 

 acquire immunity. But this phase is of very short duration. After 

 an interval, which may be measured by hours or days, the signs 

 of poisoning recur. During the period of intermission the microbes 

 seem in a resting stage, when, like the tubercle bacilli, they are 

 highly resistant to the phagocytes. In individuals belonging to 

 races which have had much experience of malaria a more per- 

 manent immunity slowly arises. Thus all, or nearly all, negro 

 children on the West coast of Africa suffer long from malaria, and 

 many perish of it, but the adults are more or less free of it. At 

 any rate, they are much more resistant. Blacks from the American 

 Islands, many of whom enter the country as soldiers in West 

 India regiments, suffer severely, and it may be fatally at first, a fact 

 which has led Koch and others to the highly erroneous conclusion 

 that no race is more resistant than any other to malaria. But 

 West Indian blacks, comparatively few of whom perish, suffer 

 much less than the white officers. If they survive for some months 



1 In syphilis the development of the rash is sometimes marked, as in measles, 

 by a rise of temperature indicative of poisoning. Indeed, the evidence of the 

 presence of toxins in syphilis is clear. See 416-418. 



