THERAPEUTIC IMMUNIZATION IN MAN 459 



Human beings are less susceptible to such mixtures than are 

 monkeys, but nevertheless more so than guinea pigs. It also appears 

 that diphtheria bacillus carriers or such persons who, because of a 

 previous infection, have antitoxin in their blood are much more sus- 

 ceptible to these mixtures than are others. Newborn children are 

 less susceptible than are children from 4 to 15 years. Mixtures 

 which are entirely neutral for the newborn may incite febrile reac- 

 tion in older children. In all cases the injection of such mixtures is 

 followed by a more or less active production of antitoxin. 



The mixtures which von Behring advocates at present are so 

 prepared that the toxin action upon guinea pigs is practically nil; 

 in other words, the mixture is completely neutralized. 



The method represents in purpose, and apparently in achieve- 

 ment, a safe process of actively immunizing against diphtheria. 

 Heretofore the method of protecting human beings prophylactically 

 against diphtheria has consisted in the injection of antitoxic serum. 

 This, unquestionably a wise procedure, has nevertheless the disad- 

 vantage of bringing about an immunity of short duration only. 

 Within 20 to 30 days the antitoxin injected may have completely or 

 almost completely disappeared from the blood stream. Prophylactic 

 immunization with the toxin-antitoxin mixtures, however, repre- 

 senting as it does an active immunization, is likely to be more pro- 

 longed in its effects. According to Behring a human being possess- 

 ing 0.01 antitoxin unit in 1 c. c. of blood may be regarded as still 

 moderately protected against diphtheria. According to his estima- 

 tion a decline to this amount, in a person actively immunized by the 

 mixtures (an estimation based upon curve measurements of treated 

 cases), would take about two years. He has observed that horses 

 that had been actively immunized by him, and subsequently used in 

 agricultural work, retained measurable antitoxin values in their 

 blood after five years without treatment. 



Schreiber 28 and others state, also, that this method of active 

 immunization with mixtures of toxin and antitoxin has the advan- 

 tage of avoiding the anaphylactic dangers incident to the injection 

 of antitoxin alone. Their opinion is probably erroneous, since it is 

 most likely that whatever anaphylactic dangers there are result from 

 the injection of horse serum rather than from the antitoxin con- 

 tained in the injected substance. Moreover, the recent studies of 

 Park have shown satisfactorily that the danger of anaphylaxis in the 

 injection of antidiphtheritic sera is practically nil. Among 330,000 

 cases on record there were but five deaths. 



The chief value of this new method of immunization is that it 

 represents a safe technique for the prophylactic treatment of indi- 

 viduals exposed to the disease and possibly for the general prophy- 

 lactic immunization of school children, nurses, physicians, etc. In 

 28 Schreiber. Deutsche med. Woch., Vol. 39, No. 20, 1913. 



