IMMUNITY, IMMUNIZATION, AND CURE. 67 



conclusion that the agglutination is not a manifestation of 

 the vital activity of the bacilli, but rather that it represents 

 a passive reaction on the part of the protoplasmic sub- 

 stance. According to a more recent statement by Kraus, 

 a mixture of immune serum with filtered cultures, after 

 exposure for twenty-four hours to a temperature of 37 C. 

 (98.6 F.), exhibits a precipitate, and sometimes even the 

 formation of flocculi. According to Gruber, the agglutinat- 

 ing substances are derived from the bodily constituents of the 

 bacteria. This statement, however, can not be sustained, 

 as agglutinating properties may be observed in the serum 

 of animals after the injection of soluble metabolic products, 

 of filtered, quite young bouillon-cultures. 



We have already stated that, as the result of his investi- 

 gations of agglutination, Gruber attempted to establish a 

 new theory of immunity. This assumes that the aggluti- 

 nating substances cause the bacterial membrane to swell, 

 and thus render the bacterial protoplasm accessible to the 

 alexins of Buchner, in consequence of which death of the 

 microorganisms is brought about. This hypothesis of 

 Gruber, however, is not supported by the facts elicited by 

 further investigation. There need be no relation between 

 agglutination and immunity. There are cases in which, in 

 spite of the agglutinating property of the serum, immunity 

 does not exist, and vice versa. Further, the assumed swell- 

 ing of the bacilli can not be demonstrated microscopically. 



4. ANTITOXINS. The anti-substances of the bodily fluids, 

 and especially of the blood-serum, thus far described, mani- 

 fest their activity, on the whole, directly against the bacteria 

 themselves. The conditions are quite otherwise with that 

 class of anti-substances that are the last to be discussed, and 

 are, probably, the most important. We have reference to 

 the substances designated antitoxins, which derive their 

 name from the fact that their energy is directed not so 

 much against the microorganisms, but rather against the 

 metabolic products (toxins) generated by them. Their dis- 

 covery in the case of diphtheria and of tetanus is the funda- 

 mental work of Behring, and the stimulus to their further 

 investigation was given especially by Ehrlich. The latter 

 found in ricin and in abrin two albuminoid vegetable 

 poisons substances presenting numerous points of resem- 

 blance to bacterial poisons, and with which some of the laws 

 of immunity can be readily studied. As a result of his 



