CALCAREOUS MANU RES— APPENDIX. 297 



the malaria of Italy, by Gaetano Georcini, of which the substance was pub- 

 lished in two different papers in the Farmers' Register, (p. 502 of vol. iv., 

 and 460 of vol. v.) In this report the author shows, by the most conclusive 

 argument and facts, that tlie irregular irruptions of sea-water over tracts 

 of marshes, or other low-grounds, of fresli-water alluvial formation, caused 

 the long continued and worst effects of malaria ; and that by simply guard- 

 ing against the entrance of sea-water, the country was restored perma- 

 nently to healthiness. He says nothing of the reverse operation, the irre- 

 gular floodings with fresh-water of silt-marshes. But what is produced 

 by the one can scarcely fail to be as well produced in the other case. The 

 mode in which the effect is produced is not attempted to be explained by 

 the learned author quoted above; nor does any explanation seem sufficient 

 to my mind. The rapid and abundant production of malaria may perhaps 

 be aided, if not entirely caused, by the luxuriant cover of fresh-water 

 plants, in the one case, being partly killed, and made ready for putrefaction, 

 by being covered by salt water ; and in the other case, in this country, by 

 a like injurious operation on the plants peculiar to salt marshes, produced 

 by the overflowing of fresh water. We know that certain plants flourish 

 best in salt and wet soil, as others do in wet soil entirely free from salt ; and 

 that respectively with these different growths, the salt and the fresh marshes 

 are heavily covered. It must follow from a sudden change in the condition, 

 from salt to fresh, or the reverse, that the health of the entire growth must 

 be greatly injured, and much of it subjected to death and decay. 



The next most fertile source of malaria, (or perhaps what is even of 

 greater malignity, for the small space occupied,) is presented in what is en- 

 tirely the work of man— the miscalled improvements made by embanking 

 and partially or entirely drying tide-marshes. The soils of these marshes, 

 as I have ascertained by careful analyses, are composed, for about half their 

 weight, of vegetable matter, and probably nine-tenths of their bulk is of 

 that material, destructible by decomposition, when circumstances are favor- 

 able to that result; and drainage and cultivation produce precisely the con- 

 dition which is most favorable. When covered twice every day by flood- 

 tide, a marsh soil of this kind, though composed of the most putrescent 

 materials, is but little subject to decomposition ; because, being always tho- 

 roughly water-soaked, even when not entirely covered, and by water con- 

 tinually changed, the air is too much excluded, and the wetness is too much 

 in excess, to favor the progress of decomposition. When the marsh rises so 

 high as not to be covered by daily or frequent tides, then decomposition 

 is more favored by the drier state of the surface, and, to a greater extent, 

 malaria is evolved, and health injured. Hence the inference, that the higher 

 and drier the marsh, the more it is injurious to health. But as soon as such 

 a vegetable and putrescent soil is made nearly dry, and still more when 

 cultivated and exposed to be penetrated by the air, decomposition proceeds 

 under the most favorable circumstances. The soil sinks annually and ra- 

 pidly, not so much by drying (as commonly supposed) as by actually rotting 

 away; and, in a few years, it is reduced to so low a level as again necessa- 

 rily to pass under the dominion and shelter of the water. The more com- 

 plete the drainage, and the more perfect the management as arable or tilled 

 land, the more rapidly is that end reached. In the progress to this end, a 

 layer of the whole soil, of from one to three feet in thickness, will have passed 

 off into the air in the gaseous products of putrefaction, of which enormous pro- 

 ducts, a large proportion will be malaria, and the effects produced by it on 

 the health of some of the neighboring population are generally so evident as 

 to leave no doubt of the source of the evil. More full details on the effects 



