418 BACTERIOLOGY. 



that by the aid of the presence or absence of this reac- 

 tion in the serum of convalescents from suspected 

 typhoid fever the nature of the disease could be deter- 

 mined. It was further found if the serum of an animal 

 thoroughly immunized to the typhoid bacillus was 

 diluted with 40 parts of bouillon, and a similar dilu- 

 tion made of the serum of non-immunized animals, 

 and both solutions were then inoculated with a culture 

 of the typhoid bacillus and placed in the incubator at 

 37 C., that after the expiration of one hour macro- 

 scopical differences in the culture could be observed, 

 which increased in distinctness for four hours and then 

 gradually disappeared. The reaction occurring is de- 

 scribed as follows : In the tubes in which the typhoid 

 culture is mixed with typhoid serum the bacilli are 

 agglomerated in fine, whitish flakes, which settle to the 

 bottom of the tube, while the supernatant fluid is clear 

 or only slightly cloudy. On the other hand, the tubes 

 containing mixtures of bouillon with cholera or coli 

 serum, or the serum of non-immunized animals inocu- 

 lated with the typhoid bacilli, became and remained 

 uniformly and intensely cloudy. These serum mix- 

 tures, examined microscopically in a hanging drop, 

 show distinct differences. The typhoid serum mixture 

 inoculated with the typhoid bacilli exhibits the organ- 

 isms entirely motionless, lying clumped together in 

 heaps; in the other mixtures the bacilli are actively 

 motile. 



These observations were made independently by 

 Gruber and Durham, who maintained, however, that 

 the reaction described by Pfeiffer was by no means 

 specific, and that when the reaction is positive the 

 diagnosis still remains in doubt, for the reaction is 



