146 Epidemics. 



functions, not only superior, but , antagonistic to the sur- 

 rounding inorganic world. Epidemic conditions are those 

 external conditions, or continuous changes, occurring in the 

 surrounding inorganic world, or the antagonism between 

 higher and lower grades of organic life, which tend to reduce 

 the products of vital power to a lower level, or to limit the 

 number of individuals, or amount of matter that is directly 

 under the sway of vital force. 



From such a point of view it is evident a wider range of 

 contingent agencies, always at work for evil or for good, in 

 relation to the applying of a given force, as vital, to bring 

 about a given result, must be taken into consideration in a 

 general and comprehensive manner. 



The sun, as the centre of our system, and the spring of all 

 vital phenomena in the vegetable world, and from thence 

 by induction to the animal world, requires a first considera- 

 tion in examining the relation of the external world to vital 

 phenomena. 



Every part of the earth, during the circle of its journey 

 round its own orbit, has exactly the same number of hours 

 and minutes of light at the poles, the Equator, or the 

 temperate regions ; but, in relation to diurnal continuance 

 of light, the greatest possible variation is attained, from 

 twenty-four hours of exclusion of sunlight in the Arctic 

 regions for a certain period of the year, and at another part 

 of the year continuous sunlight for the same space of time 

 twenty-four hours to the very moderate variation of an 

 hour or less on either side of twelve hours in the Equatorial 

 regions ; and between these points every intermediate gradua- 

 tion of time in the twenty-four hours between the seasons 

 of winter and summer. Therefore, from the amount of sun- 

 light in the year upon every portion of the globe, no inference 

 can be drawn as to health or sickness, barrenness or 

 fertility. 



