108 MAN --AN ADAPTIVE MECHANISM 



infections are old enemies. Organisms strange to 

 each other have no rules for fight. This is evidenced 

 by the high mortality which results from the introduc- 

 tion of infections into countries in which they are not 

 indigenous, so that natural selection has had no oppor- 

 tunity to protect the organism by a long series of selec- 

 tive struggles. When measles was first introduced 

 into Samoa by Europeans, it wrought a cruel havoc 

 among the natives. When la grippe was first imported 

 into Russia, it ran a severe course. In like manner, 

 many of the terrible epidemics of " plague" in ancient 

 history may have been due to the appearance of some 

 new germ or the spasmodic rehabilitation of an old one. 



Distribution of Chemical Ceptors 



The same relation which exists between contact 

 ceptors and their distribution in those parts of the 

 organism, where harm-producing agents would have 

 been encountered throughout its evolution, exists be- 

 tween chemical ceptors and the parts of the body 

 most commonly exposed to the local invasion of infec- 

 tious agents. Many of these areas, such as the skin 

 surface and the superficial organs, are identical with 

 the pain areas, but many other parts of the body, which 

 are totally devoid of the contact ceptors, are abun- 

 dantly provided with chemical ceptors for the appre- 

 hension of their own specific menaces. The surfaces 

 of the face, the neck and scalp, the extremities, 

 the eyes, the nose, the throat and the lungs, which 

 have constantly been exposed to pyogenic infections, 

 are, as one would expect, well equipped with pro- 

 tective mechanisms. The lungs, which make no re- 



