CAUSE OF CONGENITAL IMMUNITY. 97 



mental animal is always at command. In difficult cases 

 experiments in infection have also many times been carried 

 out on man. 



The causes of congenital immunity (resistance, 



Buchner) lie in protective arrangements of the organism, 

 regarding which I cannot here speak exhaustively. Only 

 so much is given as is fairly in accord with all the facts, 

 corresponding to the views formulated by Buchner as a 

 compromise to the various opposed opinions. Upon in- 

 vasion of a resisting organism by pathogenic germs, a part 

 is destroyed by pre-existing protective substances (alexins) 

 which are in solution in the serum (originating from leu- 

 kocytes) ; another part is destroyed by alexins, which are 

 produced from leukocytes (also from other tissues even- 

 tually) under the influence of the bacteria. l 



In the body the leukocytes appear to be able to live 

 while supplying these secretions; in the test-tube certainly 

 it is only possible to obtain bactericidal substances from 

 leukocytes with certainty through injury (freezing, distilled 

 water, foreign serum, toxins) (Schattenfroh, A. H. xxxv, 

 135) . The serum acts more strongly upon pathogenic than 

 upon non-pathogenic varieties (Leclef ) ; also spores may 

 be destroyed. 



Part of the organisms destroyed by the alexins are sup- 

 plementarily taken up by leukocytes, but, moreover, it is 

 undoubtedly true that at least some organisms are, while 

 living, devoured by leukocytes. Metschnikoff and his 

 pupils, moreover, insist (without, in recent times, contest- 

 ing the significance of the alexins) that the latter phe- 

 nomenon (phagocytosis) is of the highest import in im- 

 munity. Denys (C. B. xxiv, 685) has directly shown 

 that pathogenic streptococci are scarcely at all, while, on 

 the contrary, non-pathogenic ones are very rapidly de- 

 voured by leukocytes ; the absence of phagocytosis here 

 only concerns the pathogenic streptococci. 



So far the alexins have not been isolated; they are very 



1 Recently, however, Sawtchenko and Schattenfroh have commu- 

 nicated investigations, from which it follows that, at least in some 

 cases, the poly- and mono-nuclear leukocytes contain no alexin, in 

 spite of strong bactericidal action of the serum (Schattenfroh, Mliuch, 

 med. Wochenschr., 1898, No. 12, 353). 



