AGGLUTINATION. 109 



of Pfeiffer that there is an essential difference between the 

 agglutinating and the speciiic bactericidal materials. 



1. There are sera wliich in definite dilutions no longer 

 agglutinate, but yet act as bactericides in the peritoneal 

 cavity (R. Pfeiffer, Deutsch. med. Wochenschr. , 1898, No. 

 31, 489). 



2. Often an immune serum, from which all agglutinins 

 have been abstracted by long luxuriant growth of the 

 inoculated bacteria, which after sixteen hours are no 

 longer paralyzed (which, therefore, is devoid of all ag- 

 glutination), is still active in the peritoneal cavity. 



The observations may, however, be in part explained by 

 the discovery of Emmerich and Low, that in the abdomi- 

 nal cavity the action of immune sera is very much in- 

 creased b}'' the lack of oxygen (see p. 110). 



The action of agglutinin and specific bactericidal sub- 

 stances is, like that of antitoxin, in a great measure spe- 

 cific. For the bactericidal action R. Pfeiffer has main- 

 tained absolute specificity ; also other authors, as Dunbar, 

 Sobernheim, Loffler, and Abel, arrived at results that speak 

 very much in favor of specificity (compare typhoid, chol- 

 era, etc.). 



The agglutination phenomenon has been studied by very 

 many investigators, and the standpoint taken by its dis- 

 coverers has been confirmed as entirely correct. The action 

 of immune sera is strongest upon the variety against wliich 

 the immunity has been produced; less, but simihxr, against 

 related varieties (only in high concentration) ; and fails with 

 varieties that are not related. 



Thus, for example, a serum from an animal which was 

 immunized against the Bact. typhi was active in a dilution 

 of -j^Tj- upon Bact. typhi, and upon Bact. coli at ■^-^. 



It is evident that this property can be of diagnostic 

 value. 



1. If we have serum from an animal which is immun- 

 ized against true Bact. tj-phi, then it is employed to iden- 

 tify doubtful bacteria as typhoid bacteria, if the serum 

 dilution of -^ acts distinctly upon the bacteria to be diag- 

 nosticated, but not upon related bacteria ; for example, 

 Bact. coli. 



2. If one has undoubted typhoid bacteria, one can as- 



