302 



CALCAREOUS MANURES— APPENDIX. 



There is still another source of malaria, which it is necessary to touch on 

 In connexion with the above-mentioned, though it has been already treated 

 more fully elsewhere, and therefore will be but slightly mentioned here.* 



From the vegetable matter upon the driest land, as it ferments and de- 

 cays, there must be extricated more or less of the gaseous matter which, 

 when in excess, is injurious to health. According to this view, the whole 

 surface of the country, and especially that most heavily covered with vege- 

 table matter, may furnish malaria. The degree of hurtfulness of this pro- 

 duct will depend on the power of grov^ing vegetables to feed on, and of 

 the soil to absorb and fix in it this matter, which, according to its direction 

 and quantity, may either enrich land, feed plants, or poison men. In ea'lier 

 publications I have stated at large my reasons for believing that all the 

 products of vegetable decomposition, on naturally poor lands, are lost to 

 the land;t and as the ultimate results of decomposition are gaseout', or 

 aeriform, they must go off into the air. These products constitute or cause 

 malaria, and its injurious efiects on the health of the inhabitants. But cal- 

 careous matter serves effectually to fix in the soil the enriching principles of 

 decaying vegetable matter, until they serve as food for growing plants. 

 Hence the deduction that a naturally poor soil, made calcareous, will no 

 longer throw off gaseous products, or malaria, into the air ; but will store it 

 up as fertilizing manure. The sure remedy for the irregular and gene- 

 rally slight degree of sickliness thus caused, is to marl or lime all the land 

 that requires calcareous earth. But that remedy would not be sufficient, if 

 mill-ponds or marshes in the neighborhood continued to send out large ad- 

 ditional supplies of the aeriform poison.f 



The correctness of my deductions as to the very injurious effects of mill- 

 ponds on health, will be denied on several grounds, which, so far as ex- 

 pected, I will anticipate as objections, and state with the answers, as fol- 

 lows: 



Objection 1. — Admitting generally, and to some extent, the ill effects of 

 mill-ponds in producing noxious exhalations and autumnal diseases, it does 

 not appear that these effects can be either so great, or so sure, as is charged 

 above. The residents on the farms nearest to mill-ponds are not always, 

 and often not at all, more sickly than those who reside several miles distant. 

 The house of the slave who acts as miller, is usually near the mill, and close 

 to the pond ; yet families so situated are generally as healthy as any others, 

 and sometimes are healthy in a remarkable degree, compared to the neigh- 

 borhood generally. 



Ansiver. Near the mill-dam, or the lower end of the pond, may well be 

 less affected by the exhalations from it, than places a mile or two more dis- 

 tant. That part is the deepest of the pond, and of which also the banks 

 are steepest ; and perhaps half a mile in length of the bottom of the upper 

 and shallowest part .of the pond, and of alluvial mud, might be left naked 

 in drought, before a margin of steep hill-side of three feet width could be 

 exposed near the mill. Further — from the greater lightness of the malaria, 

 it will rise high in the air, and would soon be carried flir away by a mode- 

 rate bre€ze. If the wind be moderate, and steady to one direction, and 

 still more if its course be confined to an opening by or between woods, or 

 to a narrow valley between high hills, it may well be imagined that the 

 poisonous air might injuriously affect persons perhaps five miles from the 

 pond, and who would not suspect the operation of so distant a source ; 



* See 'Essay on Calcareous Manures,' 3d ed., chapter xv , and 'Essay on the Police 

 of Health" commencing; p. 154., vol. v., of Farmers' Register, 

 t Essay on Calc. Man., pp. 23, 57 and 89. 



