CHAPTER XIII. 

 PASSIVE IMMUNIZATION. 



WHILE active immunization is the procedure par excellence to be 

 employed for prophylactic purposes, or in the treatment of those 

 infections which are characterized by a chronic course, the indi- 

 cations for passive immunizations are essentially afforded by the 

 acute infections, the idea being that in these the necessary time may 

 not be available for the formation of protective antibodies, or that 

 these are not furnished in sufficient quantity by the infected organism 

 itself. The plan, then, is to introduce these principles from without, 

 either in the form of antitoxic sera or of bacteriolytic-bacteriotropic 

 sera, as the case may be. That such sera may at times be serviceable 

 also for prophylactic purposes goes without saying, but it is natural 

 that their value from this standpoint should be limited. For whereas 

 in the actively immunized organism the entire defensive mechanism 

 is thrown into action, and remains in action, often for a considerable 

 length of time, the protective principles which we introduce from 

 without are after all limited in quantity, and are, no doubt, elimi- 

 nated or destroyed after a relatively short time. If such sera are 

 administered at a time, however, when the organism has just become 

 infected, or is immediately threatened with infection, their use is 

 unquestionably rational, and frequently of great value. 



As regards the mode of action of the two types of sera, which are 

 available for passive immunization, I would merely recall that those 

 organisms which are strong toxin producers are also of a low grade 

 of infectiousness, and that the macroorganism can usually overcome 

 the infection as such without much difficult}', if it is protected 

 against the harmful effect of the toxins. In tetanus the infection 

 is indeed usually already under control before the toxins, which 

 have been liberated, can exercise their fatal action. With the true 

 parasites and semiparasites, on the other hand, where toxins either 

 play no role or only a limited role, the bacteriolytic sera would, 

 a priori, be expected to be of service, but, unfortunately, their actual 



