672 BACTERIOLOGY. 



of specific affinities beyond those common to what may 

 be termed proteolytic enzymes in general ; and Buchner 

 regards it as nothing more than the normally present 

 " alexin," to which he called attention years ago. 

 Whether these objections be well taken or not, whether 

 the doctrine as a whole can be accepted or not, the experi- 

 mental data on which it is based warrant the opinion 

 that it is the only satisfactory working hypothesis that 

 has been offered in explanation of the mechanism of 

 what Buchner years ago designated the "reactive tis- 

 sue-changes " underlying the establishment of acquired 

 immunity.' 



The observations serving as the basis for this doctrine 

 have given to the blood and fluids of the body a new 

 and peculiar interest. According to circumstances, there 

 may be detected in the blood and tissue-juices a number 

 of bodies having totally different functions and affinities, 

 and therefore presumably different from one another. 

 To summarize briefly : First, there is normally present 

 in the blood-serum of practically all animals the de- 

 fensive "alexins" already mentioned. Second, the 

 antitoxins that are found in the blood of animals arti- 

 ficially immunized from special sorts of infection and 

 intoxication, as well as occasionally in the blood and 

 tissues of normal animals, the functions of Avhich are 

 susceptible of demonstration outside the body as well as 

 within the tissues of tlie living animal. Third, a body 

 possessed of disintegrating, bacteriolytic powers, a bac- 

 teriolysin — i. e., having the property of actually dissolving 

 bacteria, so that the phenomenon may be observed under 



1 Justice cannot be done to the beauty anrl ingenuity of tliis con- 

 ception in so brief a summary as is appropriate to a text-book. It must 

 be read as it came from its authors, to be appreciated. 



