LYSINS, AGGLUTININS, PRECIPITINS, ETC. 231 



called "thread-reaction" of Pfaundler. 1 This consists in the forma- 

 tion of long convoluted threads of bacterial growth in the hanging drop 

 of dilute immune serum after twenty-four hours. Very strict specificity 

 is attributed to this reaction by Pfaundler. 



Agglutinins act upon dead as well as upon living bacteria. For the 

 microscopic tests bacterial emulsions killed by formalin were intro- 

 duced by Neisser. 



Ficker 2 has recently succeeded in preparing an emulsion of typhoid 

 bacilli, which is permanent and may be kept indefinitely, and may be 

 employed for macroscopic agglutinations. 3 



Attention has been called by various workers to a source of error in 

 all these methods, known as pseudo-dumping. 4 The causes for such 

 clumping not due to agglutinins seem to lie in the presence of blood cells 

 in the serum or excessive acidity of the culture medium. 5 In fact, ag- 

 glutination of bacteria by acids in definite concentration can be carried 

 out and seems to depend directly upon the hydrogen ion concentration. 



While the microscopic methods are more suitable for clinical-diag- 

 nostic purposes, because of the smaller amounts of blood required, the 

 macroscopic tests are far preferable for the purposes of bacterial differen- 

 tiation and research. Greater exactitude of dilution is possible when 

 dealing with larger quantities; microscopic unevenness in the bacterial 

 emulsion does not become a source of error; and positive and negative 

 reactions are more sharply defined. 



Nature of Agglutinins. Gruber and Durham, 6 the discoverers of ag- 

 glutinins, at first advanced the opinion that the agglutinins were iden- 

 tical with the immune body concerned in the Pf eiffer reaction, which by 

 injuring the bacteria rendered them susceptible to the alexins. Pfeiffer 7 

 and Kolle 8 soon showed, however, that by the addition of cholera vibrio 

 to immune serum, the agglutinins could be completely absorbed, or used 

 up, while bacteriolytic substances still remained. The same authors 

 demonstrated that immune serum, preserved for several months, would 

 lose its agglutinins without a corresponding loss of bacteriolytic power. 

 It has been variously shown since then, by these and other authors, 

 that the agglutinins and the bactericidal substances are in no way parallel 



1 Pfaundler, Cent. f. Bakt., xxiii, 1898. 2 Ficker, Berl. klin. Woch., 1903. 



3 Exact method of production of "Ficker's Diagnosticum " is a proprietary secret. 



4 Savage, Jour, of Path, and Bact., 1901. 



6 Biggs and Park, Amer. Jour, of Med. Sci., 1897; Block, Brit. Med. Jour., 1897. 

 6 Loc. cit. 7 Pfeiffer, Deut. med. Woch., 1896. 



8 Pfeiffer und Kolle, Cent, f . Bakt., xx, 1896. 



