AUTOINFECTION. 45 



Snake venoms, and the poisons of spiders, bees, 

 and various insects, are toxins of animal origin 

 which have pathologic and scientific importance. 



4. "Endogenous" infection or "autoinfection." AU*O- 

 By this term we mean infection of an individual Inection - 

 by micro-organisms which reside naturally on 

 some surface of the body. Such organisms pro- 

 duce infection only when some other factor, par- 

 ticularly traumatism, comes into operation. 



Hair follicles frequently contain staphylococci 

 and when occlusion occurs the organisms may pro- 

 duce a pustule or a furuncle. An injury of the 

 conjunctiva may result in infection by staphy- 

 lococci or pneumococci, which are present normally., 

 and many wound infections are due to organisms 

 which pre-exist on the surface. 



Probably a factor of great importance for the 

 invasion of such organisms is a condition of low- 

 ered resistance on the part of the tissues. We 

 know, for example, that virulent streptococci and 

 pneumococci are frequently found in the pharynx 

 and on the tonsils in apparent health. Exposure 

 to cold in some instances may be the means of 

 lowering the resistance of the surfaces (inhibition 

 of the antibacterial forces) so that the organisms 

 become more numerous and penetrate the sur- 

 face. Observations suggest also that the presence 

 of a serous exudate, such as exists even in a tran- 

 sient inflammation, may cause an increase in the 

 virulence of the organisms which are bathed by it. 

 Similar forces may play a role in the bronchitis 

 and pneumonia which follow exposure. 



There seems to be comparatively little danger of 

 "autoinfection" from pathogenic bacteria which 

 exist normally in the intestinal tract, except in 



