39 



On Malaria, No. II. 



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



Having pointed out, in the former paper on this subject, the 

 nature of the soils or places, of whatever description, by -which 

 malaria is generated, it remains to notice a few other circum- 

 stances connected with its natural history, a knowledge of 

 which is essential for the purposes of prevention ; and finally to 

 describe such modes of prevention, applicable to these several 

 circumstances, as have been found useful in guarding against 

 the attack of diseases from this cause. Under the first head, 

 there remain to be considered, the effects of climate and season ; 

 the changes which occur in the production and propagation of 

 malaria, from various natural and artificial causes ; and also, 

 the various modes in which it is propagated. 



It has already been remarked, that a certain elevation of 

 temperature was necessary to the production of this poison, 

 though what the precise degree is, has not been ascertained; 

 and as this is, chiefly, what distinguishes the regions or periods 

 of the year which generate malaria, I need not make two divi- 

 sions of season and climate. If, however, this temperature is 

 not fixed, it will perhaps suffice for our present purposes to say 

 that the greater part of Scotland, whether as to climate or 

 season, seems incapable of generating the disease from this 

 cause ; though there are exceptions of a permanent nature, or 

 exceptions of climate, as was perennially true of the Carse of 

 Gowrie before its drainage ; while there are others which happen 

 when, as in the last year, there has been a pecuharly hot 

 summer, and which are exceptions of season. 



And thus it is as to more northern regions; where a hot 

 summer becomes more than an equivalent for an average low 

 temperature ; as an example of which, there is no place where 

 intermittents are more severe and abundant than at Stockholm. 

 But the extreme of evil from this cause occurs, as is well 

 known, in the tropical climates; appearing almost proportioned 

 to the heat of the climate, and what is important to observe 

 to the moisture also. The destructive effects of certain parts of 

 Africa, India, America, and so forth, are famiharly known ; and 



