HOSACK ON THE LAWS OP CONTAGION. 235 



A similar interval has been frequently noticed in the history of the 

 plague. Dr. Russell, in his account of the plague of Marseilles, in 

 1720, observes, "that from the 12th of July to the 23d there was a 

 deceitful pause, during which the popular apprehensions began to sub- 

 side. The physicians were reproached with ignorance in having mis- 

 taken ordinary fevers for the plague. The disease, however, in this 

 interval, had continued to spread in the street, Rue de l'escale, where it 

 made its first appearance."* 



It has also been remarked of the plague, as well as of the yellow 

 fever, that the infection spread most rapidly when the atmosphere was 

 not only heated and loaded with moisture, but when it was least agitated 

 by wind or thunder storms. During those calms, when the air may be 

 said to be relatively at rest, it has been uniformly remarked, that the 

 contagion of the yellow fever has multiplied itself most extensively, as 

 was always very apparent by the greater number that were seized within 

 five or six days after such close weather had been observed, all which 

 circumstances certainly conspire to promote the fermentative process 

 that has been contended for. 



This is not all : whenever the yellow fever has been introduced into the 

 cities of the United States, its first extension has always been slow and 

 gradual. Upon several occasions its boundaries have been accurately 

 defined by our board of health. This, as I have stated on a former 

 occasion, was remarkably the case in this city in 1805. The disease, 

 in that year, was confined, for some weeks, to a small portion of the 

 •astern side of the city, and, as stated by the board of health, " not a 

 case occurred, in any part of the town, that was not referable to that as 

 its source. "f This fact being ascertained, the board accordingly for- 



Hi»tory of the Plague. f Hardie'a Account of the Malignant Fever of 1 805. 



