230 HOSACK ON THE LAWS OF CONTAGION. 



impure air of the city, or of the infected spot, were uniformly observed 

 to be most susceptible of the contagion. Those, too, who enjoyed the 

 most vigorous health, and the most robust constitutions, the reverse of 

 that condition of body which would be the effect of a residence in im- 

 pure air, were more readily infected upon coming into the atmosphere 

 impregnated with the contagion, than those who had remained con- 

 stantly exposed to its influence. Whatever differences of opinion have 

 existed among the physicians of the United States, as to the origin of 

 the disease, they are all perfectly agreed relative to the facts which I 

 have just stated. Indeed, Dr. Chisholm himself inadvertently admits 

 the same to be true ; for he observes, that in the West Indies, sailors, 

 soldiers, and young men, especially those who have recently arrived 

 from Europe, and are least accustomed to the climate, were more 

 obnoxious to it than others.* 



Dr. Gordon, and, indeed, all the most distinguished practical writers 

 on this subject, concur in the same observation. " New comers," says 

 Dr. Gordon, in the appendix to Dr. Chisholm's late valuable letter to 

 Dr. Haygarth, " were infected with the pestilential fever, while the old 

 seasoned soldiers had only the common tropical remittents; and this was 

 universally the case whenever both diseases were at the same time epi- 

 demic"! A similar, and still more general, observation on the predis- 

 position of those who are unaccustomed to impure air, is made by Dr. 

 Blane. " Infection," says he, " like some other poisons, does not so 

 readily affect those who are accustomed to it, and therefore those who 

 are in the habit of being exposed to it, frequently escape its bad effects." 

 For the like reason, he adds, " physicians and nurses are less suscep- 

 tible than others ; and strangers, who are accustomed to a pure air, are 



* Cbisholm'a Letter te Haygartb, p. 182, &c. f Ibid. 2?0. 



