BACTERIOLYSINS AND H&MOLYSINS 133 



because, after all, when we immunize an animal 

 against a certain bacterium we do not produce 

 merely a bactericidal serum, but one which con- 

 tains agglutinins, precipitins, opsonins, and per- 

 haps still other antibodies as well. The use of 

 specific anti-bacterial sera has been tried in man both 

 to cure existing infections and as a preventive of 

 infection. The therapeutic use has in most instances 

 been rather disappointing, though in dysentery, 

 plague, gonococcus and meningococcus infections 

 the results have been somewhat better. Recently 

 also, fairly good reports are heard from the admin- 

 istration of large doses of antistreptococcus serum. 

 In susceptible animals injections of some of the 

 very virulent bacteria, as pneumococci, strepto- 

 cocci, typhoid bacilli and cholera spirilla, can be 

 robbed of all danger if small doses of their respective 

 sera are given before the bacteria have increased to 

 any great extent in the body. If given later they 

 are ineffective. Conditions in man are probably 

 very similar. 



The reasons for the failure of these antibacterial 

 sera when used therapeutically demand a moment's 

 consideration. It is apparent from all that has 

 gone before that a deeper insight into the mechan- 

 ism of immunity discloses many difficulties to be 

 overcome before we can hope for much in a practical 

 way. In the case of the bacteria sera, for example, 

 we have as yet found no method of increasing the 



