INFECTION AND IMMUNITY. 541 



which act, so to speak, as antidotes to these poisons. If 

 the tissue-elements are not of sufficient vigor to destroy 

 the invading bacteria or to render inert the poisons pro- 

 duced by them, the bacteria are victorious and infection, 

 in different degrees of severity, results ; on the other 

 hand, if there be failure to excite disease, the tissues are 

 victorious, and are then said to be resistant to or immune 

 from this particular type of infection. 



In some cases the protective bodies possessed by the 

 animal act directly upon the invading organisms them- 

 selves — i. e., they are germicidal ; in others their func- 

 tion is more that of antidotes, or neutralizers in the 

 chemical sense, of the poisons produced by these organ- 

 isms, the organisms themselves, in certain instances, 

 experiencing only slight injury from a limited sojourn 

 in the living tissues. For those constituents of the 

 animal body that are by nature endowed with germi- 

 cidal peculiarities, the designations "alexins" (Buchner) 

 and " defensive proteids " (Hankin) have been sug- 

 gested. Their nature has not been determined, but the 

 fact that their destructive action is characterized by a 

 solution or disintegration of the bacteria leads Buchner 

 to regard them as proteolytic (bacteriolytic) enzymes. 



To those ill-defined substances whose affinities are 

 restricted to the soluble toxins elaborated by the invad- 

 ing bacteria the name "antitoxins" is now generally 

 applied. Contrary to what we have seen in the case of 

 the normally present alexins, antitoxins are but rarely 

 to be detected in the normal animal organism. When 

 they do exist under such conditions, they are of but 

 comparatively feeble potency.^ In the great majority 



^ See Bolton : Transactions of Association of American Physicians, 

 1896, vol. xi. p. 62. Pfeiffer : Deutsche med. Wochenschrift, 1896, 



