104 



* 



localities and climates. The most notable examples of this kind are 



influenza and cholera. 



In respect to these three kinds of epidemics, the following laws 



are well ascertained: — 1. That their prevalence is periodical. 2. 

 That no two of them, belonging respectively to different classes, 

 and the same is generally true of such as belong to the same 

 class, occur to the same extent, in the same place, at the same 

 time. 3. That whenever any of the diseases belonging to the several 

 classes prevail together in the same place, they become -involved in 

 each other in the order we have arranged them, the first being modi- 

 fied by the second, and both of these by the third, so that one is 

 always predominant, and compels the others to wear its livery. 4. 

 That the same epidemic varies in its character in different years, the 

 modifications depending mostly upon the diversities of the seasons, 

 and the varying influences of the prevailing insensible meteoration, 

 or, as it is called, the epidemic constitution of the atmosphere. 



It might not be unprofitable to exhibit the facts and reasonings 

 on which the above classification of epidemics is based; and to illus- 

 trate, by examples, the operation of the laws just stated. But re- 

 strained from this by the need of brevity, we proceed to observe, that 

 we are not aware that any well characterized meteoratious epidemic 

 has occurred within the United States during the last year. Whilst 

 the influenza and cholera have prevailed in some parts of the Old 

 World, neither of them has appeared in the New. The only diseases 

 which, on account of their prevalence, have attracted general atten- 

 tion, in the period referred to, are a few of those arranged in the 

 divisions of contagious and infectious epidemics. 



In respect to contagious epidemics, the committee are not able to 

 state the extent of their occurrence in the various cities and states 

 of the Union. There are, however, in our possession some facts re- 

 lating to the epidemic history of scarlet fever, measles, and small- 

 pox, as they have prevailed in the city of New York, during a long 

 series of years, which are, perhaps, worthy of recital. 



The New York bills of mortality are, for the most part, complete 

 from the commencement of 1805 to the end of 1847. For several 

 years, so far as is known, prior to 1805, and from this period for- 

 ward to the close of 1822, scarlet fever was very rarely met with, 

 and measles and small-pox were comparatively infrequent. Between 

 these two epochs, that is, during eighteen years, there were reported 

 only 43 deaths from scarlet fever, 339 from measles, and 719 from 

 small-pox. After 1822, these diseases slowly assumed an epidemic 



