294 



On Malaria, 

 [Communicated by J. Mac Culloch, M. D., F.R.S., &c. &c.] 



It Is a familiar fact, not merely to physicians, but to the people 

 at large, that there is produced from marshy lands a peculiar 

 substance, called marsh miasma, in physic, and to which Italy 

 has given the term Malaria ; from the effect of which on the 

 human body, there are excited fevers of different characters, 

 but generally divided under the two great leading heads of m- 

 termittentaxid remittent. What the chemical nature of this sub- 

 stance is, has not been discovered, though numerous experi- 

 ments have been instituted for this purpose ; yet, with respect 

 to its properties, we know enough to believe that it is a com- 

 pound gas, decomposable by certain agencies, a,nd also capable 

 of being conducted to certain distances from the place of its 

 production, by the winds. Further, it is ascertained that it can 

 be condensed or accumulated in particular places ; that it can 

 form a certain attachment to the soil, or to peculiar solid 

 bodies, although this is not permanent, as happens with respect 

 to the matter of contagions ; and lastly, that it is particularly 

 affected, both in respect to its propagation and production, by 

 certain qualities of the atmosphere, consisting in its conditions 

 as to temperature and hygrometrical moisture. 



Thus, although ignorant of its nature, we are in possession of 

 certain facts appertaining to its natural history, which we can 

 convert to use in warding off its evil influences, or preventing 

 the attacks of the diseases which it produces ; while, if one 

 class of precautions depend on this knowledge, the other con- 

 sists in that remaining branch of its natural history, which re- 

 lates to the causes through which it is, in the first instance, 

 produced, and in the next, propagated. 



Being, as I have remarked, produced by marshy lands very 

 especially, it has been naturally concluded that its immediate 

 cause was the mutual action of vegetables and water, though it 

 has been disputed in what that precise action consisted. To 

 ascertain this is, however, of some importance, as on the nature 

 of that action must, in a great measure, depend under what 

 particular circumstances it is produced ; consequently, what 



