THERAPEUTIC IMMUNIZATION IN MAN 481 



that the milder cases are materially benefited by the treatment, and it 

 is not at all impossible that in such cases aggravation of a milder 

 case into fatal septicemia may be prevented by the timely adminis- 

 tration of the plague serum. Animal experimentation also seems to 

 indicate that the administration of the serum may be of great value 

 as a prophylactic measure. It seems, on the other hand, as far as we 

 can judge from the evidence of statistics, that when a case of plague 

 has developed into the condition of active septicemia the administra- 

 tion of even the strongest plague sera at present available is of little 

 use. And this is indeed unfortunately true of all passive immuniza- 

 tion where the activity of the serum seems to depend chiefly upon 

 bactericidal and opsonic properties. For we cannot definitely accept 

 at the present day the claims that a true antitoxic serum, in the sense 

 of those produced against diphtheria and tetanus poisons, can be 

 really produced in the case of plague. The toxic substances derived 

 from plague bacilli by a number of observers do not correspond in 

 many particulars to true toxins. 



FACTS CONCERNING ACTIVE PROPHYLACTIC BOCTJNIZATION 



IN MAN 



In a previous chapter we have dealt with the treatment of in- 

 fectious disease with emulsions of dead bacteria or vaccines. The 

 discussion there was confined to the use of these substances in the 

 case of developed disease in which the infectious agent had already 

 gained a foothold in the body. Concerning this form of therapy 

 much difference of opinion exists, and we have seen that careful 

 judgment must be applied to the selection of cases to which treatment 

 with vaccines is adapted. 



Concerning the prophylactic immunization of human beings with 

 bacteria there can be little difference of opinion ; this procedure finds 

 its justification in prolonged laboratory experience in the hands of 

 many men since the days of Pasteur. 



The principle of specifically increasing the resistance of an in- 

 dividual by treatment with an altered form of the disease, either 

 with the attenuated bacteria, with dead bacteria, or with bacterial 

 extracts, has been sufficiently discussed in Chapter IV. It is indeed 

 surprising that this phenomenon of prophylactic protection, though 

 discovered by Jenner in small-pox, and developed by Pasteur in 

 rabies, did not find more general application to the diseases of man 

 until recent years. At present such methods are in extensive use in 

 typhoid fever, in which they have had unquestionably excellent re- 

 sults. In the cases of cholera and plague numerous attempts have 

 been made, but the results here are not as clear-cut as they have been 

 in the case of typhoid. In the succeeding paragraphs we have set 



