OF INFLUENZA. 795 



of which are brought by the immediate influence 

 of external cold. If owing to a change of wind, 

 the temperature is suddenly reduced 10 or 20 

 over a large extent of country, the disease be- 

 comes more violent, and assumes the character 

 of a wide spreading epidemic, termed influenza, 

 which prevails occasionally at all seasons, but is 

 generally much milder and of shorter duration in 

 summer ; because at that season, the reduced 

 temperature that brings it on, is soon followed by 

 warm weather.* When it comes on with a cold 

 northern or eastern wind, after the powers of life 

 have been diminished by a hot summer, and the 

 prevalence of a malarious atmosphere, it assumes 

 the type of a more malignant fever, ushered in 



* It has been often asserted by medical authors, that epidemic 

 influenza is not brought on by cold, nor vicissitudes of temperature, 

 because it sometimes appears during summer. But in temperate 

 climates, the transitions from heat to cold are often greater and 

 more sudden during summer than winter. Nor is it surprising 

 that the disease should exist in the tropical portions of India and 

 Africa, when we reflect that the diurnal temperature of those re- 

 gions varies from 30 to 50. Dr. Dieffenbach maintains, that 

 epidemic influenza is generated in the middle latitudes of the 

 northern hemisphere, by a peculiar miasma, originating in the 

 northern portions of Europe, Asia, and America. He also states, 

 that in Europe, it spreads from the north east to the south west, 

 with the speed of the prevalent wind, and diminishes in violence 

 with the distance from its origin. However this may be, it may be 

 asserted with confidence, that in no climate nor season, is the 

 imaginary miasma competent to produce the epidemic, without a 

 reduction of temperature ; and it is well known to be most preva- 

 lent when the fluctuations of temperature are greatest and most 

 frequent. 



