4 i 8 THE POPULAR SCIENCE MONTHLY. 



only 98 deaths from malarial fevers. In 1869 they rose to 128; in 

 1870, to 213; in 1871, to 291; and in 1872, to 348: an increase of 

 350 per cent, in four years. Since then some diminution in their fatal- 

 ity has occurred. They occasioned 282 deaths in 1873, 295 in 1874, 

 and 275 in 1875. 



Let us now consider under what circumstances malaria may he 

 produced. Although it cannot be denied that there are peculiar local- 

 ities where, with apparently every presumed condition existing for the 

 development of malaria, that poison is entirely absent, yet the concur- 

 rence of malarial emanations with such conditions in innumerable 

 places establishes beyond a question their direct relation. The essen- 

 tial element in the production of malaria would appear to be vegetable 

 decomposition ; and, in order that this process shall ensue, the simul- 

 taneous operation of air, moisture, and a certain high range of tem- 

 perature, is absolutely required. Localities, therefore, where such com- 

 bination occurs, are prolific of malaria. Of this character are swamps 

 and morasses, alluvial deposits, loose, porous, sandy, and argillaceous 

 soils, or deep, loamy, marly lands underlaid by impermeable strata 

 affording capacity for the retention of moisture, regions exposed to 

 periodical or occasional inundation, places left bare by the subsidence 

 of lakes or drying up of streams, and particularly areas subject to 

 the intermingling of salt and fresh water as salt-marshes into which 

 fresh streams discharge, or regions liable to tidal overflow and re- 

 cession. 



The exhalations from marshy tracts are recognized by their effects 

 upon the human system throughout the world ; and the fact that 

 marshes bear a causative relation to malaria has been demonstrated in 

 numerous instances by the disappearance of fever after thorough 

 drainage and cultivation, and its reappearance upon their being al- 

 lowed to relapse into neglect. The favorable effect of drainage and 

 cultivation is owing both to the systematic removal of water near the 

 surface, and most probably also to the absorption by the growing 

 crops of the products of organic decomposition. On the same prin- 

 ciple Prof. Maury succeeded in antagonizing the noxious emanations 

 from a marsh surrounding the observatory at Washington by planting 

 it thickly with sunflowers, which seem to possess an extraordinary ab- 

 sorbing power. Sebastian is inclined to believe that the Calamus 

 aromaticus which grows in some swamps has a similar neutralizing 

 quality. Swamps covered with water are not so dangerous as those 

 partially dry, the layer of water serving as a protection against the 

 access of air and heat to the vegetable matter underneath. 



A certain continuous range of temperature seems essential to the 

 development of malaria, which is almost unknown beyond 60 north 

 and 57 south latitude, and during the cold season in the temperate 

 zone. According to Hirsch, it prevails up to various degrees of lati- 

 tude and average annual temperature. It is the average summer tem- 



