DEFENSIVE FACTORS OF THE ANIMAL ORGANISM 251 



The formation of antitoxins directed against soluble poisons, how- 

 ever, did not explain the immunity acquired by animals against 

 bacteria like Bacillus anthracis, the cholera vibrio, and others which, 

 unlike diphtheria and tetanus, produced little or no soluble toxin. 

 It was evident that the antitoxic property of immune blood serum 

 was by no means the sole expression of its protective powers. Much 

 light was shed upon this phase of the subject by the discoveries of 

 Pfeiffer in 1894, who worked along the lines suggested by the inves- 

 tigations of Nuttall and Buchner. Pfeiffer 35 showed that when 

 cholera spirilla were injected into the peritoneal cavity of cholera- 

 immune guinea-pigs, the microorganisms rapidly swelled up, be- 

 came granular, and often underwent complete solution. The same 

 phenomenon could be observed when the bacteria were injected into 

 a normal animal together with a sufficient quantity of cholera-im- 

 mune 36 serum. 



This process he observed microscopically by abstracting, from time 

 to time, a small quantity of the peritoneal exudate and studying it 

 in hanging-drop preparations. The reaction was specific in that the 

 destructive process took place to any marked extent only in the case 

 of the bacteria employed in the immunization. 



Metchnikoff, 37 Bordet, and others not only confirmed Pfeiffer's 

 observation, but were able to show that the lytic process would take 

 place in vitro, as well as in the animal body. The existence of a 

 specific destructive process in immune serum was thus established 

 for the vibrio of cholera and soon extended to other microorganisms. 

 The constituents of the blood serum which gave rise to this destructive 

 phenomenon were spoken of as b act erioly sins. 



Following closely upon the heels of Pfeiffer's observation came the 

 discovery of another specific property of immune serum by Gruber and 

 Durham. 38 These workers noticed that certain bacteria, when brought 

 into contact with the serum of an animal immunized against them, 

 were clumped together, deprived of motility, and firmly agglutinated. 

 They spoke of the phenomenon as agglutination and of the substances 

 in the serum giving rise to it as agglutinins. 



The list of antibodies was again enlarged by Kraus, 39 who in 1897 



35 Pfeiffer, Zeit. f. Hyg., xviii, 1894. 



36 Pfeiffer und Isaeff, ibid. 



87 Metchnikoff, Ann. de 1 'inst. Pasteur, 1895. 



38 Gruber und Durham, Munch, med. Woch., 1896. 



w Kraus, E., Wien. klin. Woch., 32, 1897. 



