232 HOSACK ON THE LAWS OF CONTAGION. 



-are thereby rendered capable of renewing the same process in other bo- 

 dies under similar circumstances. This process has very properly been 

 denominated by Dr. Walker, the assimilating fermentation,* and has 

 been no less successfully employed both by him and by Mr. Cruik- 

 shank,f as well as by Dr. Cullen, to explain the changes which take 

 place in the living system, acted upon by small pox, and the virus of 

 other contagious diseases, than it has been by Sir J. Pringle,J Mac- 

 bride^ and Alexander,|| to the phenomena of fermentation, as it occurs 

 out of the body.H The history of plague, dysentery, and typhus fever, 

 as well as the recent observations in animal chemistry, furnish a variety 

 of facts which may be adduced in illustration of such fermentative pro- 

 cess taking place in the atmosphere, and in watery fluids loaded with 

 the excretions of the human body, or the vapours of vegetable and 

 animal substances in a state of putrefaction. 



Similar facts, illustrative of the fermentative process contended 

 for, have been observed whenever the yellow fever has prevailed in 

 any of the cities or towns of the United States. I have already 

 stated that this disease has always prevailed in proportion to the 

 presence of such fermentable materials. It is no less true, that 

 whenever the disease has been introduced it has spread in the greatest 

 degree in those seasons when the air was unusually moist : this was re- 

 markably the case in New-York, in 1795** and 1798,tt and in Philadel T 

 phia, in 1793 and 1798 -.It and that the yellow fever has prevailed in 

 the United States in those seasons when the heat, combined with mois- 

 ture, was most favourable to such assimilating or fermentative process 



* Walker's Inquiry into the Small pox. t Anatomy of the Absorbing Vessels. 



\ Diseases of the Army, Appendix. § Experimental Essays. || Experimental 



Essays and Experimental Inquiry. H See Note H. ** See Bayley on the Yellow 



Fever of 1795. ft Hardie on the Yellow Fever of 1798. ft See Rush and Cum*. 



