(J74 ACUTE INFECTIOUS DISEASES. 



being very favorable to decomposition of vegetable substances, and 

 hence uncommonly favorable for the development of malaria, and for 

 its spread from places where it always exists to others that are gen- 

 erally free from it; but they appear to be due to other unknown 

 causes, which also favor the development of malaria, or to an extension 

 of the disease from its point of origin to distant places by currents of 

 air. We do not know why, but great epidemics of intermittent have 

 often preceded epidemics of Asiatic cholera. In hot countries, cholera 

 and intermittent, and, still oftener, dysentery and intermittent (see 

 next chapter) frequently prevail at the same time. 



The sporadic occurrence of intermittent is most curious. Those 

 cases where persons affected with malaria move from places where ma- 

 laria is prevalent, and continue to present the symptoms of infection 

 for a time after settling in their new home, are not to be counted as 

 sporadic. But, both in city and country, cases occur where the persons 

 could not have been infected elsewhere. There is no explanation for 

 these cases, except the supposition of very limited foci, which are 

 harmless for persons outside of them, or of a very diluted miasm, which 

 only affects a few persons who are peculiarly disposed. There is not 

 the least ground for the supposition that, under some circumstances, 

 intermittent may result from other causes than from infection with 

 malaria. 



Every age, both sexes, and all constitutions, have a predisposition 

 to intermittent fever, and the greater or less tendency to the disease, 

 in various persons, does not depend on the constitutional differences to 

 which it has been referred, but to other only partially understood in- 

 dividual peculiarities. Exhausting exercises, and other debilitating 

 influences, errors of diet, and particularly catching cold, increase the 

 predisposition so much, that persons, who have long been exposed to 

 malaria with impunity, are not affected by it till one of these causes 

 has acted on them. The same explanation must answer for those 

 cases where persons who have escaped the disease in malarious places 

 are attacked by it after leaving them. Then the infection has evi 

 dently taken place earlier, but has not shown its effects in the person 

 who was little disposed to the disease, and has not caused injurious 

 results till the necessary predisposition was induced by other noxious 

 agents. Among the influences that increase the predisposition to 

 intermittent, the most evident is one or more previous attacks of the 

 disease, which is just the opposite of the case in the acute exanthe- 

 mata and typhus. There is .only an accommodation of the organism 

 to the poison to the extent that persons who have been exposed tc 

 it for some time have a chronic disease with enlargement of the 

 spleen, without fever, instead of having intermittent fever. The 



