THE PHENOMENON OF AGGLUTINATION 219 



occurrence can be observed, each one particularly adapted to some 

 special purpose for which the reaction is carried out. Gruber and! 

 Durham, who were investigating the properties of bacteriolysins 

 when they observed agglutination, naturally recognized the specific 

 nature of the reaction and proposed to make use of it for the purpose 

 of bacterial differentiation and species determination. For this pur- 

 pose, which has become one of the most important of the practical 

 applications of the agglutination reaction, the phenomenon is best 

 observed by the so-called "macroscopic method," in which a series 

 of serum dilutions are mixed, in small test tubes, with equal volumes 

 of emulsions of the bacteria. Thus, if we wish to determine the 

 nature of an unknown bacillus, suspected of belonging to the typhoid 

 bacillus group, by this meth- 

 od, we may determine its ag- 

 glutination in the serum of 

 an animal immunized with 

 a known strain of typhoid. 

 The tubes are incubated 

 after the mixtures have been 

 made, and the agglutination 

 which has taken place in the 

 various tubes is recognized 

 by a clearing up of the fluid 

 and the flaking of the bac- 

 teria after from one to three 

 hours. The test tube method 

 has the advantage of permit- 

 ting the use of larger quanti- 

 ties of reagents than can be 

 used in the other methods 



described below, and therefore more exact quantitative measurements 

 can be made. 



Although this method for the determination of bacteria has found 

 universal application, it is probably most frequently employed at the 

 present time for the rapid identification of colonies of doubtful 

 typhoid or dysentery, incident to the isolation of these organisms for 

 stools by such methods of plating as those of Conradi-Drigalski, of 

 Endo, or of Hiss. The suspicious colonies can thus be fished directly 

 to an agar slant, and the cultures, when developed, emulsified and 

 identified by agglutination. The advantages of such a method for 

 the determination of the biological interrelationship of the organ- 

 isms of a given group, like, for instance, that of the dysentery bacilli, 

 are obvious. 



An ingenious use of this reaction was also made by Shiga when 

 he determined, among various bacteria isolated from the stools of 

 dysentery cases, the particular one which was specifically aggluti- 



MICROSCOPIC AGGLUTINATION. 



