THEORIES OF IMMUNITY. 



bacteria, either dead or rendered inoffensive by 

 the previous action of the body fluids. 



: The humoral theory made many converts in 

 all parts of the world, and was and is very 

 generally accepted. It has, however, been 

 queried by a few observers whether the phe- 

 nomena seen to take place in the test-tube 

 really are the same as those that occur in the 

 living* body tissues, and it has been shown that 

 similarity of action does not uniformly exist. 

 It has been shown many times that the blood of 

 animals susceptible to infection is bactericidal 

 to the specific bacteria of that infection; while 

 on the other hand, the blood of animals not 

 susceptible to such infection has absolutely no 

 bactericidal properties towards the specific bac- 

 terium. Such parodoxes as this are not at all 

 uncommon in the case of infections already 

 investigated, and are so common as to form an 

 almost insurmountable obstacle to a belief in 

 the general action of the body fluids in the pro- 

 duction of immunity." (Metchnikoff, I. c.) 



In reference to what has just been said, as 

 long ago as 1889 (Cent. f. Bakt., 1889, T. VI., 

 pp. 481, 529) Lubarsch carried on a long series 



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