HO SACK ON THE LAWS OF CGNTAGIOIN. 231 



the most susceptible of any."* With these facts and observations 

 before us, we are compelled to conclude, that the impure air necessary 

 to propagate the contagion does not operate in the manner Dr. Chisholni 

 supposes, by " increasing the susceptibility of the system to the action 

 of the poison introduced." On the contrary, I believe that it produces 

 its effects by some chemical combination with the peculiar virus 

 secreted from the diseased body, and that thereby the contagion 

 becomes more or less extensively multiplied, according to the extent 

 and virulence of such vitiated atmosphere. 



I shall not attempt to define the precise nature of the chemical 

 union which takes place under such circumstances. But I wish it to 

 be distinctly understood, that in such combination, I do not believe 

 with those writers who contend that a tertium quid is produced, or, as 

 Dr. Adams of London, in his late publication on Epidemics, has 

 reiterated the same idea, " that a new kind of air is generated."! On 

 the contrary, as far as I am enabled to view the subject in connexion 

 with the facts usually observed during the prevalence of the diseases 

 which have been noticed, I am inclined to believe, that in this combina- 

 tion the peculiar virus of those diseases is in no way changed, but mul- 

 tiplied ; and that this multiplying power is a process very analogous to 

 that which we observe to take place in the assimilation of the fluids of 

 the human body to the peculiar taint which may be introduced into the 

 system, as, for instance, in small pox and syphilis ; or, perhaps, that it more 

 nearly resembles the process of fermentation, as it occurs in inanimate 

 matter. By both these processes such an assimilation takes place in the 

 fluids acted upon, whether of the living body or in dead matter, that they 

 partake of the same properties with the virus or ferment introduced, and 



* Diseases of Seamen, p. 228. i Adams on Epidemics, p. 11, 



