294 CALCAREOUS MANURES— APPENDIX. 



during the siege, had written a treatise on the diseases of the country, he 

 would have been better prepared to treat of them than most of those who 

 have essayed such taslis; and he probably would have considered as a 

 regular disease of the country the fatal "jail-fever," which swept off in 

 numbers the absconding slaves who had joined the British army, and were 

 crowded together in Yorktown until the surrender, and which form of 

 disease has never been known in Virginia before, or since. 



All agree that decaying and putrefying vegetable matter is one of the 

 greatest, if not the only source of malaria. Of course, then, in addition to 

 the sufficient abundance of the material, the circumstances most conducive 

 to its putrefaction must be the most favorable to the production of malaria. 



The presence of moisture, a certain degree of heat, and the access of 

 air, are circumstances essential to putrefaction, and of course to the pro- 

 duction of malaria; and neither can take place without the aid of all three 

 of these things. Much moisture would be less favorable than a less quan- 

 tity ; and entire covering by water would, by e.vcluding air, nearly prevent 

 fermentation, and its consequence, the formation and escape of malaria. 



It is also one of the few settled points, among scientific investigators, that 

 malaria is very light, at least when warmed by the sun ; and hence tiie fact 

 known to many in this country, that those who live on the borders of 

 marshes, and of mill-ponds, sometimes escape all injury from their exhala- 

 tions, when others, who live on high hills, and at much greater distances 

 from the sources, sulfer greatly by tlie disease produced. Facts of this 

 kind are numerous, and of regular annual occurrence, in Gloucester county. 

 The whole of the wide and very level low-grounds furnish residences very 

 healthy, compared to the tide-water region in general ; though intersected 

 in every direction by tide-waters, and though there still remains much 

 swamp land unreclaimed, such as the whole body of low-ground was when 

 in a state of nature. But the high, dry and hilly land, which forms the ridge 

 of the county, is less healthy; and the highly elevated and beautiful sites'of 

 mansion-houses overlooking the low-grounds are universally sickly in 

 autumn. 



If all the facts in regard to the action of malaria were as regular and 

 uniform as this one just stated is in Gloucester, there would be far less 

 doubt on the subject. It is the uniform character of that county, in its 

 high-land, low-ground, and also the water, and the long extent of each, 

 which causes these effects to be so uniform there. Owing to causes stated 

 in the description of the low-grounds of Gloucester, (Farmers' Register, page 

 178, vol. vi.,) there is but little malaria evolved there; and if that, as sup- 

 posed, rises by its greater levity, the regular daily sea-breeze must cause 

 it to float towards the high-lands ; and the long and regular line of ridge 

 cannot fail to receive it, and in not very different proportions. But in most 

 other situations, even though malaria should be produced in great quantity 

 and with direful effects, yet these effects are so extremely irregular, in the 

 places, the times, and the intensity of their operation, that they cannot be 

 certainly traced to their true source ; and therefore, that source may re- 

 main scarcely suspected, while it is dealing out death somewhere in almo.st 

 every season. Away from the vicinity of the sea, nothing can be more 

 irregular than the winds ; yet, supposing a mill-pond to produce a regular 

 and large supply of malaria every autumn, (though that supply is itself 

 extremely irregular,) it depends upon the direction," force, and continuance 

 of every change of wind, whether and where, and to what extent the 

 malaria will produce disease. It is therefore not at all strange, nor opposed, 

 as is thought by some, to the regular annual production of malaria or 

 Dauses of sickness by each mill-pond, that the visitations of sickness, at any 



