THE BIOLOGY OF HEALTH 153 



often to the waste-products of food which has been 

 unused or imperfectly used within the body, or to 

 other waste-products which are in a more direct way 

 the ashes of the living fire. 



No Disease in Wild Nature. — This seems the place 

 to notice a fact which should make us think and act ; 

 that there is almost no disease among wild animals. 

 Wild animals grow old, but they are never senile. Wild 

 animals have many parasites, but with most of these 

 they have established live-and-Iet-live relations. Epi- 

 demics due to microbes sometimes occur, but almost 

 always because man has interfered, e.g. by taking ani- 

 mals to new surroundings where they encounter mi- 

 crobes which they are not adapted to resist, or by 

 killing o& the natural eliminators of the weakly, or by 

 permitting over-crowding, or by infecting soil and 

 water. What, then, of salmon disease, fowl cholera, 

 grouse disease, swine fever, and so on through a dreary 

 list? These occur in more or less artificial, humanly 

 contrived conditions ; and the same is probably true 

 of plant diseases. It is not asserted that variations 

 in the direction of weakness and abnormality and 

 disturbed vital processes may not occur among wild 

 animals, but they seem to be rare and they are sifted 

 out before they take grip. Disease in wild nature 

 is a contradiction in terms. Why, then, is it that 

 Man has diseases always with him? Because many 

 human activities and surroundings are so artifi- 

 cial and injurious, because modern Man has poor 

 resting instincts and feeding instincts (Man does not 



