672 



ACUTE INFECTIOUS DISEASES. 



chiefly in marshy regions, and in such places the number of 

 persons affected increases or decreases according as circumstances favor 

 or do not favor the decomposition of dead vegetable matter in the 

 marshes. If it grow very cold, so that the marshes freeze up, the in- 

 termittent fever ceases. The same thing occurs when, in dry seasons, 

 the marshes entirely dry up, or if, in very wet seasons, a thick layer 

 of water protects the mouldering bottom of the marsh from the action 

 of the sun and air. On the other hand, in marshy regions, hot seasons, 

 if not too dry, so that the sun's rays can act freely on the exposed but 

 still moist bottom of the marsh, are characterized by the great preva- 

 lence of intermittent fever. It is uncertain whether the decomposi- 

 tion of certain vegetables, or a peculiar quality of the water, favors the 

 development of malaria more than other causes. A mixture of sea- 

 water with spring and rain water which occurs in marshes near the 

 ocean, from high tides or heavy winds forcing the sea-water into the 

 marshes so-called brackish water, appears to be peculiarly injurious, 

 because many fresh-water plants, as well as many marine plants, con- 

 tained in the mixture, cannot thrive in it, and consequently die and 

 decompose. Malarial fever is endemic in low lands near rivers, which 

 are flooded yearly, just as in marshy regions. No especial explanation is 

 necessary to show that this flooding also causes the death of quantities 

 of vegetable matter, which subsequently decomposes when exposed to 

 great heat. Intermittent fever occurs where land has lain for a long time 

 uncultivated, and is then broken and tilled again, from the same causes 

 as it does in marshy regions ; for here, too, quantities of dead vege- 

 table matter are brought up and undergo decomposition. Lastly, in 

 some cases where intermittent fever occurs under apparently opposite 

 circumstances, that is, when it is very dry, it has been shown that 

 the soil was rich in subsoil water, and that, under a dry, porous sur- 

 face, parched by the summer heat, there were subterraneous swamps. 

 These common peculiarities, which appear in most of the regions where 

 malarial fever prevails, do not, however, as was before said, justify us 

 in concluding that malaria is a chemical body, an organic or inorganic, 

 a solid or gaseous product, formed by the decomposition of vegetable 

 substances. On the contrary, the non-occurrence of intermittent fever, 

 in some typically swampy places, and its appearance in some places 

 where extensive or specific putrefaction would be most unlikely to 

 take place, seem to indicate that while the conditions peculiar to 

 swamps, marshes, etc., favor the development of malaria, they are not 

 a sine qua non, nor do they alone suffice to induce the disease. This 

 view is even more strikingly supported by the observations that all 

 the persons drinking water from a certain swamp were taken sick with 

 intermittent fever, as these observations contrast with a large number 



