PHENOMENA FOLLOWING IMMUNIZATION 89 



but took place regularly when true cholera strains, from various 

 sources, were used in the experiment. The immunity of cholera- 

 treated animals, therefore, was found to be an antibacterial and not 

 an antitoxic one. Cholera spirilla introduced into a normal animal 

 were permitted to multiply and accumulate until a sufficient number 

 were present to furnish, upon cell death, a fatal dose of poison. In 

 immunized animals the small quantities of bacteria first introduced 

 succumbed rapidly to the lytic properties of the serum and accumu- 

 lation was prevented. 



By these experiments, now commonly spoken of as the "Pfeiffer 

 Phenomenon," it was definitely proved that active immunization 

 with bacteria incites in the serum of the treated animal a potent in- 

 crease of bactericidal properties an increase which is entirely spe- 

 cific in that the bactericidal power toward bacteria other than those 

 employed in the immunization does not exceed the normal. The 

 immunity in these cases, then, is not antitoxic, but rather "antibac- 

 terial" and depends on the development, in the immune sera, of anti- 

 bodies quite distinct from the "antitoxins." These immune serum 

 constituents were spoken of by Pfeiffer as "bacteriolysins" or "spe- 

 cific bactericidal substances." 



Not long after the discovery of the specific bacteriolysins another 

 property of immune sera was described by Gruber and Durham. 37 

 They had been studying bacteriolytic phenomena with colon and 

 cholera organisms, and noticed that these bacteria were rapidly ag- 

 glomerated and gathered in small clumps when emulsified in homolo- 

 gous immune serum. Similar clumping had indeed been described 

 before. Metchnikoff, Isaeff, Washburn, and Charrin and Koger had 

 described it on various occasions, but had not recognized it as a 

 specific property of immune serum. 38 Gruber and Durham studied 

 it carefully, determined that it was present to a degree roughly pro- 

 portionate to the degree of immunization attained, and that its 

 specificity was such that it could be utilized for bacterial differen- 

 tiation. They believed that the substances in the immune serum 

 responsible for this agglutination were independent of other serum 

 constituents and applied to them the term " agglutinins." 



The problems of immunization had now considerably expanded 

 and the nature of the new serum reactions was assiduously studied. 

 Primarily the phenomenon of agglutination was regarded as a part 

 of the struggle of the body against the living bacteria and Gruber 

 himself believed that it depended upon a swelling or "klebrig wer- 

 den" of the micro-organisms which tended to cause their sticking 

 together, and rendered them more readily amenable to the action of 

 the bactericidal powers of the serum. Bordet, 39 however, early con- 



37 Gruber and Durham. Munch, med. Woch., 1896. 

 as y or references see chapter on Agglutinins. 

 39 Bordet. Ann. Past., 1896. 



