HOSACK ON THE LAWS OF CONTAGION. 227 



manifestly prove the specific character of those diseases, and that they 

 are propagated by a specific secretion peculiar to each disease, whether 

 it be plague, dysentery, typhus, or yellow fever. Indeed, to use the em- 

 phatic expression of the Edinburgh Reviewers on this subject; " In the 

 present state of medical knowledge, it would not be at all more absurd 

 to deny the existence of fever altogether, than to maintain that it is not 

 propagated by contagion."* But, in the language which Dr. Mead has 

 applied to the plague, we may say of all the diseases of this class, " that 

 a corrupted state of the air is, without doubt, necessary to give these 

 contagious atoms their full force."t 



If it were necessary I might go on to cite every return of the yellow 

 fever with which the United States have been visited to show, that the 

 progress of the pestilential poison has ever been commensurate with 

 the impurities of the atmosphere, and that when sufficiently diluted 

 with pure air, it ceases to propagate itself. 



It is probably owing to this impure condition of the atmosphere 

 that the various fevers, and the greater mortality of diseases in general, 

 are to be ascribed, which physicians have frequently observed to pre- 

 cede the appearance of pestilential disorders, and to announce their 

 approach, and which have led many to conclude that the pestilence 

 itself was thus engendered by local circumstances, and not imported. 

 Facts of this nature have served to mislead the editors of the Medical 

 Repository, and many other late writers, who thus confound the exciting 

 and predisposing causes of disease ; who do not discriminate between 

 the inflammable materials, and the spark which lights the flame; but 

 have identified the domestic circumstances which have served to diffuse 



* Edinburgh Review, vol. 1. p. 246. \ Mead's Medical Works. 



