MALARIA. 421 



Besides the localities enumerated, malaria is apt to be induced or 

 intensified in a region wholly or comparatively exempt from it be- 

 fore, during the disturbance of large extents of soil, as in the construc- 

 tion of canals, roads, railways, fortifications, and dikes, rooting out 

 of timber, preparation of virgin land for cultivation, etc. Vegetable 

 organisms previously hidden and protected underground are thus 

 brought to the surface and exposed to the agencies of putrefaction. 

 Laborers engaged in such works and the neighboring inhabitants soon 

 suffer. The " polders " of Holland, those parts reclaimed from the 

 sea by the erection of dikes, are of this character, and the workmen 

 engaged on them are attacked with malarial troubles of great severity. 

 In this country such instances are common. We have an example at 

 our very doors in the increase of malarial fevers which accompanied 

 the opening of the new boulevards, and the engineering excavations 

 of the Harlem Railroad. After such works have been completed, 

 however, it is not unusual for the vicinity to be restored to health- 

 fulness. 



It must be acknowledged that occasionally miasmatic fevers ap- 

 pear and disappear without there having occurred any perceptible 

 changes in the relations of the soil. Such circumstances were re- 

 ported to the Pennsylvania State Medical Society as having been 

 noticed in 1856 along the Juniata River. Reports to the Connecticut 

 State Medical Society also mention the appearance of miasmatic 

 disorders without any recognized cause in portions of the State pre- 

 viously exempt from them. 



There would appear to be some connection between such phe- 

 nomena and the fluctuating level of the subsoil-water as affected either 

 by rainfalls or subterranean forces. According to Jilek's figures, in 

 Pola, a noted malarious district of Istria, between 1863 and 1868 the 

 number of persons attacked by fever varied from fourteen to fifty- 

 one in every one hundred inhabitants, in exact proportion as the 

 rainfall had varied from one to eighteen inches. 



We know that the level of the ground-water is constantly changing. 

 It rises and falls more or less rapidly, and at different rates in differ- 

 ent places in some only a few inches either way annually, but in 

 many places several feet. In Munich, its limit was found by Petten- 

 kofer to be about ten feet. In India, the changes are greater. At 

 Saugor, in Central India, the extremes are between a few inches from 

 the surface during the rains, to seventeen feet in May. At Jubbulpore 

 it varies from two to fifteen feet from the surface. The causes of such 

 changes are rainfalls, pressure of water from seas or rivers, and ob 

 struction of outflow. The pressure of the Rhine has been observed 

 to affect the water in a well 1,670 feet distant from the river. An 

 impeded outflow which raises the level of the ground-water has been 

 productive of an immense spread of paroxysmal fevers. Demster, 

 Taylor, and Ferguson, have reported such to have been the case in 



