218 The Atmosphere in relation to Malaria. 



common occurrence possess a highly putrid type, as yellow 

 and intermittent fevers ; but where the principal defect in 

 the climate is the existence of great accumulations of 

 vapour in the atmosphere, scurvy is the prevalent malady. 

 Thus, in Choco, where rain constantly falls, it is an un- 

 common circumstance to meet with an individual who is 

 not affected with this complaint. 



On the elevated plains of the Andes, on the contrary, 

 where the atmosphere is extremely dry, the inhabitants are 

 subject to violent attacks of ophthalmia, as the children 

 of the African desert. 



In all marshy countries, the inhabitants recommend the 

 same precautions, in order to prevent the accession of the 

 endemic disease. From America to India, the traveller is 

 directed carefully to avoid exposing himself to the evening 

 dew. 



Moscati took advantage of his knowledge of this fact, 

 and endeavoured to insulate the miasma dissolved in the 

 air over the rice fields of Tuscany, by condensing it along 

 with the dew. He observed in the condensed liquid small 

 flocks, which possessed all the properties of animal matter, 

 while the water, in the course of a few days, began to 

 putrify. 



In 1812, M. Rigaud de I'lsle made a series of experi- 

 ments in the marshes of Languedoc with the same object 

 in view. He condensed the dew upon glass. It exhibited 

 the same appearances as that examined by Moscati ; but, 

 in addition, it afforded a precipitate with nitrate of silver, 

 which rapidly assumed a purple colour. But he endea- 

 voured to prove that such dew was hurtful to animals 

 when taken internally, which was attempting too much, 

 because it is sufficiently obvious, that cattle pasture on 

 marshy herbage without suffering the slightest incon- 

 venience. 



In 1819, Boussingault remarked, while engaged in a 

 geological excursion through the department of Ain, that 

 sulphuric acid, when placed in the immediate vicinity of a 

 marsh, became speedi^ black, while at a distance from the 

 puirifying source it was not altered. At this period, fever 

 was raging in the neighbourhood, and, hence, he concluded, 

 that the change in the acid was produced by the agency of 



