246 INFECTION AND RESISTANCE 



It is difficult to explain Friedberger's results. Possible impurity 

 of his preparations and the presence of traces of electrolyte seem 

 to be excluded by the fact that he was quite conscious of this possi- 

 bility of error and used only substances which yielded no ash on 

 combustion. 



It may be that the results of Friedberger in which glucose and 

 asparagin were used may have brought about agglutination by an 

 entirely different mechanism from that which we are discussing and 

 form no analogy to this. 



In one of the preceding paragraphs we have mentioned the phe- 

 nomenon spoken of as "acid agglutination." By this is meant the 

 spontaneous clumping, not only of bacteria, but of small particles of 

 any kind, in suspension, in the presence of certain concentrations of 

 acid. Michaelis, 74 Beniasch, 75 and others who have studied this 

 phenomenon in detail have come to the conclusion that it is the con- 

 centration of the hydrogen ions which is responsible for the ag- 

 glutination. This explanation is also applicable to the agglutination 

 often observed about the anode when bacteria are subjected in sus- 

 pension to the action of a direct current. In such experiments the 

 organisms after concentrating at this electrode often flocculate, and 

 it is here, of course, that hydrogen ions are present in the greatest 

 concentration. How this takes place is problematical, but the reason- 

 ing of Pauli, if applied to this, would favor the assumption that the 

 weakly charged bacteria group themselves about the ions and, when 

 a sufficiently large aggregation has formed, fall to the bottom as 

 precipitate. This phenomenon of acid agglutination is of course 

 entirely different in nature from the specific serum agglutination 

 which we are discussing. Nevertheless, Schidorsky and Reim, 76 

 Jaffe, 77 and others have attempted to apply acid agglutination to the 

 isolation and differentiation of bacteria, on the conception that dif- 

 ferent species are agglutinated by varying concentrations of hy- 

 drogen ions. The former investigators, even, claim to have been 

 successful in isolating typhoid bacilli from the stools by this method 

 in that the typhoid bacillus was agglutinated by concentrations of 

 acid which had no effect upon the Bacillus coll. Sears 78 has gone 

 over this work carefully, and, while he has obtained results which 

 bear out the contention that the agglutination is probably due to the 

 concentration of the H ions, his experiments have revealed an irregu- 

 larity in the behavior of bacteria of the same species in acid solutions 

 and an overlapping of those of one species with those of another. 

 Therefore the use of acid agglutination for differential purposes 



74 Michaelis. Folia Serol, 7, p. 1010, and Deutsche med. Woch., 37, 969. 



75 Beniasch. Zeitsckr. f. Imm., Vol. 12, 1912. 



76 Schidorsky and Reim. Deutsche med. Woch., Vol. 38, p. 1125. 

 T7 Jaffe. Arch. f. Hyg., Vol. 76. 



78 Sears. Proc. Soc. of Exp. Biol. and Med,, 1913. 



