252 INFECTION AND IMMUNITY. 



The Effect of In a preceding chapter micro-organisms were 



Bactericidal -,.. T 7.,., ,1 , - , 11T 



on divided, first,, into those which secrete soluble tox- 

 ns. ^^ immunization with which causes the forma- 

 tion of antitoxins, and, second, those which do not 

 secrete such toxins and for which no manipula- 

 tions known at the present time are successful in 

 stimulating to the formation of antitoxins. These 

 lines, however, can not be drawn sharply, for there 

 are a few micro-organisms which, according to 

 manipulation, cause the formation of either an 

 antitoxic serum or a bactericidal serum. In gen- 

 eral it may be said that the character of the serum 

 depends on the bacterial constituent which is used 

 for immunization. If the diphtheria bacillus it- 

 self, or the pyocyaneus bacillus, is injected, the 

 toxin having been washed away, bactericidal ser- 

 ums are formed, whereas if toxins alone are intro- 

 duced, antitoxins are the result. After all, it 

 seems plain that the bacteria of the second group 

 must be pathogenic, because of toxic substances 

 which they carry with them into the body. In 

 view of the fact, however, that they do not secrete 

 soluble toxins in culture media, it is held that 

 their toxic properties are integrally associated with 

 the bacterial protoplasm; they are the endotoxins 

 spoken of previously. 



The question naturally arises: Does a bacteri- 

 cidal serum in dissolving or killing its homologous 

 organism neutralize the endotoxin at the same 

 time? On the basis of very positive experiments 

 which have been performed, especially by Pfeiffer, 

 it is evident that the serum has no such action. In 

 the experiment of Pfeiifer, one may inject into the 

 abdomen a sufficient quantity of anticholera serum 



