226 H0SAC1C ON THE LAWS OF CONTAGION. 



as secreted from the diseased body, is alone, in sufficient quantity, or pos- 

 sesses a sufficient degree of virulence, to reproduce such diseases; or, 

 that by means of the impurities collected about the diseased individual, 

 occasioned by inattention to cleanliness and change of clothing, the 

 retention of his excretions, or the confined air of his apartment, the 

 virus itself becomes multiplied, and thereby the means of communicat- 

 ing the disease from one to another are in the same degree increased : 

 for it is a fact not to be questioned, that instances of yellow fever, as well 

 as of the plague, dysentery, and typhus fever, have been occasionally 

 infectious, even in the more pure air of the country, though it must be 

 acknowledged that such cases are of rare occurrence. 



It is observed by Dr. Rush, whose records of the several visitations 

 of the yellow fever in the city of Philadelphia will be lasting monu- 

 ments of the facts which they contain, as well as of the impressive and 

 eloquent manner in which they are related, " that out of upwards of one 

 thousand persons who have carried this disease into the country from 

 our cities, there are not more than three or four instances to be met 

 with of its having been propagated by contagion."* Such instances, 

 however, have occurred in New Hampshire, as related by Dr. Spal- 

 ding ;t in Connecticut, as stated by Dr. William Moore of this city ; J on 

 Staten-Island, in 1798, as recorded by Dr. R. C. Moored at Hunting- 

 don, on Long Island, in 1795 and 1798 ;|| and at Germantown, in the 

 vicinity of Philadelphia, as related by Dr. Wistar.1T But these very 

 exceptions, if they can with propriety be denominated exceptions, 



* Observations on the Origin of the Yellow Fever of 1799, p. 12. 



f Med. Repos. vol. 3. p. 8. J Addoms' Disser. p. 7. American Med. and Phil. Reg. vol. 

 2. p. 177. § Ibid. vol. 2. p. 22. || Ibid. vol. 3. p. 191. 



TT Additional Facts and Observations by the College of Physicians of Philadelphia, p. 36.— 

 See Note F- 



