CALCAREOUS MANURES— APPENDIX. 293 



fruitful sources of malaria, and to bring the whole, or very nearly the 

 whole of Virginia, to a state as healthy as that of any other country in the 

 world. If such a result is indeed attainable, it is worth making every 

 possible exertion for; and nothing will induce the smallest exertion, either 

 by the people or the government, except a full exposure of the enormity of 

 tlie evil which presses upon the country. 



It is not my purpose to attempt to investigate the cause and trace the 

 mode of operation of malaria. Though worthy of every care and labor 

 as a scientific question, it is one which as yet has entirely baffled every 

 attempt at exposition. But though it is as yet unknown what is the 

 chemical character of this subtle fluid, and what are the precise circum- 

 stances under which it is evolved, and what is the manner in wliich it 

 exerts its baneful influence— still the main and most important points admit 

 of no question. Thus, and in general, all persons, from the most ignorant 

 to the most learned, agree that there is someihi?}^ which rises into the at- 

 mosphere in hot weather, from marshy ground and stagnant waters, which 

 tends to produce the common autumnal fevers in those who are much ex- 

 posed to breathing the air contaminated by this admixture. 



Though I speak of malaria as an aeriform fluid, or gaseous product, it is 

 not designed to found my argument upon tlie truth of that opinion. Though 

 for convenience, as well as because ixiclining to the belief, malaria is here 

 spoken of as a material aeriform product, yet, it may be also used as a 

 term to designate the particular condition of drcmnslances produced by 

 certain causes, which condition operates to produce and strengthen autum- 

 nal diseases. Still less do I mean to maintain that malaria, even if material, 

 is of any one kind of gas, or any particular combination of several kinds. 

 Besides these, there are many other common points on which the learned 

 investigators of malaria totally disagree; and so much does each one insist 

 upon deducing general principles from his own particular facts, (or sup- 

 posed facts,) and so slightly and incorrectly have such facts been observed, 

 that the general reader becomes lost in the contradictory positions of 

 different instructers. Thus, judging from particular and isolated observa- 

 tions, with some writers, there is no condition of circumstances which will 

 not sometimes in a warm climate produce malaria; and with others, upon 

 equally partial and imperfect observation of other facts, the production is 

 denied to be usually caiised by any of the circumstances which arc gene- 

 rally deemed the most certain and fruitful sources. One writer, periiaps, 

 has known an exemption from disease in those who lived close to a stinking 

 marsh, or a stagnant pond ; and hence he denies that these are sources of 

 malaria, and accordingly searches for them in other circumstances. Another 

 has known the effects of malaria on troops encamped in a high defile in 

 the mountains of Spain, where the soil was dry and stony, and no water 

 except rapidly flowing rivulets, and the place some miles distant from the 

 nearest marsh or lake. Hence he concludes, that even such a locality as 

 this, in certain (unknown) circumstances, throws out abundance of malaria. 

 Considering the circumstances, under which most of the works on malaria 

 have been written, it would be strange if they were not quite contradictory. 

 The authors of most of them were army-surgeons and pliysicians, who 

 observed the effects of malaria in some deadly region, upon soldiers not 

 at all acclimated. Perhaps the author was confined to a garrison, or at least 

 limited in his observations to the line of march of an invading army; and 

 in a country to which he was totally a stranger, and among a hostile people, 

 whose opinions he could not learn, and whose language he probably did 

 not understand. If a physician of Lord Cornwallis' army, who had merely 

 accompanied his march through Virginia, and been cooped up in Yorktown 



