296 On Malaria. 



expended and dead portions ; or wherever fragments of plants 

 are exposed to moisture ; or wherever mud, impregnated with 

 invisible or dissolved vegetable matter exists ; or, finally, where- 

 ever any chemical compound of the vegetable elements is 

 wetted or held in solution in water, there the poison in question 

 may be, or will be produced, provided the temperature be suffi- 

 ciently high : and it is this necessity for a certain temperature, 

 which is the cause why that peculiar decomposition of vegeta- 

 bles which forms peat, does not produce malaria, however it 

 may occur in peaty lands, because, generally speaking, the 

 formation of peat is limited to climates or regions of a low tem- 

 perature. The nature and cause of the exception now made 

 will be explained immediately. 



I need not attempt to inquire further into the nature of this 

 decomposition, since there are no facts on which to found an 

 inquiry. What we must conclude, is, that some of the vegetable 

 elements are let loose and re-combined into a new gaseous 

 compound, while experiments carefully conducted (as ought 

 not to be doubted when Vauquelin has been engaged in them) 

 have not detected even the presence of such a new substance 

 in the atmosphere of marshes, far less its nature. It is, how- 

 ever, evident that it cannot be any of the hydrocarburetted or 

 other chemical gases which it has, at different times, been 

 supposed ; while, remaining thus in darkness, the only test of 

 its presence continues to be the effects as to disease which it 

 produces on the human body. 



But, as I remarked, we possess enough knowledge of its na- 

 tural history to assist us in guarding ourselves against its effects ; 

 and as that question, utility, is the object of the present paper, I 

 will proceed to describe as much of that as is admissible in so 

 limited a space. To know all the classes or kinds of places 

 which are capable of producing malaria, is the first and main 

 object as to prevention : to know by what means it is propa- 

 gated is the next, while the contingent circumstances necessary 

 to its production, or to its effects on the body, consisting chiefly 

 in temperature and moisture under various modes, will also de- 

 mand attention. All these things being known, we have laid the 

 preliminary knowledge, requisite to prevention, as far as that is 

 in our power ; without them, we are subject to those hazards 



