822 GENERAL LAWS OF EPIDEMICS. 



and fuel among the poor, induces them to block 

 up every chink and aperture by which the car- 

 bonic acid exhaled from the lungs of many indi- 

 viduals, occupying the same room, is prevented 

 escaping, and fresh air from entering, until the 

 air becomes exceedingly noxious. And it is 

 certain, that during hot weather, fever is often 

 produced by the exhalations of men in previous 

 good health, when thickly crowded together in 

 prisons, transport ships, barracks, workhouses, 

 and the confined dwellings of large towns. At 

 the same time, it is still more certain, that fever 

 is often produced by cold and vicissitudes of tem- 

 perature alone, without the influence of malaria, 

 or any other cause, as might be exemplified by 

 innumerable cases, which mark the progress of 

 pneumonia, pleurisy, and other inflammatory af- 

 fections, brought on by exposure to cold. 



From the foregoing facts and observations, it 

 must be evident, that the diseases of mankind 

 obey the same laws which govern all the other 

 phenomena of nature. If the vast and extremely 

 complex science of meteorology were thoroughly 

 understood in all its multifarious details, we 

 should be able to comprehend why one season 

 differs from another in temperature, direction of 

 winds, and quantity of rain, in any given place ; 

 and to predict those now mysterious revolutions of 

 the atmosphere which seem to return at certain 

 periods, as shown by the myriads of insects that 



