170 INFECTION AND IMMUNITY. 



tion and destruction of toxins in the case of anti- 

 toxic immunity. 



It is now known, as stated, that an immune 

 and opsonins. erum f av0 rs phagocytosis because of its action on 

 the bacteria rather than on the leucocytes; hence 

 the position of MetchnikofFs "stimulins," which 

 were supposed to stimulate the leucocytes to an 

 increased phagocytosis, does not seem to be on a 

 good footing at present. The value of the opsonins 

 in passive immunity is, indeed, an unknown fac- 

 tor; the question is hardly determined finally. 

 Some of the opsonins deteriorate very quickly; 

 hence they could be of no value in serums as they 

 are placed on the market. Others are more resist- 

 ant, and may have a certain value in passive immu- 

 nization, although they probably do not approxi- 

 mate in importance the bactericidal and antitoxic 

 substances. 



Summary. summar y we ma y ga y 



dal substances, antitoxins and opsonins are the 

 known and demonstrable factors in active immun- 

 ity. It does not follow that all three factors come 

 into play in every conceivable infection; or that if 

 they do, in some particular disease, the three are 

 equally important. Thus, in typhoid fever, the 

 serum has an enhanced bactericidal power, and 

 investigations seem to show that the opsonins are 

 also increased; on the other hand, we have no 

 evidence to show that acquired immunity to 

 typhoid fever is antitoxic. In diphtheria and teta- 

 nus, the immunity is represented by the presence 

 of antitoxins in the serum, whereas the opsonins 

 bacteriolysins appear to be of less importance. 

 Another condition is found in infections with 

 staphylococci, streptococci, pneumococci and some 



