HOSACK ON THE LAWS OF CONTAGION. 22& 



of the air upon the peculiar virus of those diseases ; that " it does not 

 proceed from the impure atmosphere becoming assimilated to the 

 poison introduced. 



That air, deprived of its due proportion of oxygen, and loaded with 

 mephitic materials, especially the confined excretions of the human 

 body, will vitiate the mass of circulating fluids, and impair the functions 

 of the nervous system, cannot be denied; that the febrile diseases with 

 which the system may be affected while in this state, will acquire an 

 extraordinary degree of malignancy, will also be readily conceded; but 

 that such condition, either of the atmosphere, or of the human system, 

 increases its susceptibility to be acted upon by the virus of those con- 

 tagious diseases, composing the third class, does not correspond either 

 with the facts which have fallen under my own observation, or with those 

 I have been enabled to obtain from the writings and observations of 

 others. 



The well known facts relative to the communication of jail fever 

 to the judges presiding at the Black Assizes, in 1577,* and a similar infec- 

 tion being communicated to the judges on the bench, and other persons 

 present, at the sessions held at the Old Bailey, in 1750, while the priso- 

 ners themselves remained in health, insensible to infection, furnish incon- 

 testable evidence of the effects of habit in diminishing the sensibilitv t© 

 the poison of fever: and with regard to the yellow fever, it assuredly has 

 not been the case in the United States, that those who were most accus- 

 tomed to the impure air of the place in which the disease prevailed, 

 were more susceptible of the disorder than those who had recently arriv- 

 ed from the pure air of the country, or from the more elevated parts of 

 the town. On the contrary, those who were least accustomed to the 



* Bacon's Works, vol. 2. Stowe's Chronicle. — See Note Cr. 



