148 STUDIES IN IMMUNITY. 



to the agglutinin. In this respect he agrees with Gruber's inter- 

 pretation which we shall consider later. 



Paltauf's interpretation, which would explain the agglutination 

 of bacteria by a retraction of a precipitate (Kraus) forming in the 

 fluid and collecting bacteria in its own clumping, meets with grave 

 objections. To begin with Kraus' phenomenon of precipitation 

 docs not occur constantly: even when it does occur the precipitate 

 is never abundant, and is formed so slowly that it seems incredible 

 that it occurs before the rapid and energetic bacterial agglutination 

 and is, therefore, the cause of it. Moreover no one has been able 

 to demonstrate a coagulum about agglutinated bacteria. Dincur, 

 indeed, has repeatedly attempted to find one unsuccessfully, and 

 he very correctly states that if there were such a coagulum enclos- 

 ing the bacteria we might expect to demonstrate it since coagula 

 take basic colors as shown by Nicolle. 



Certain other observations may be noted at this point. Rabbits 

 which have received several intraperitoneal injections of defibri- 

 nated hen blood give a serum which has an agglutinating and dis- 

 solving power for hen corpuscles. This active serum has still 

 another property. When mixed with hen serum it caused a pre- 

 cipitate to form in the fluid which gradually increases and finally 

 flocks out. This property of forming a precipitate with the causa- 

 tive serum present in the serum of animals injected with this serum 

 was noted recently for the first time by Tchistovitch at the Pasteur 

 Institut. Tchistovitch found that the serum of rabbits which had 

 received several injections of eel serum caused this latter serum to 

 become cloudy; he noted the same occurrence with the serum of 

 rabbits immunized against horse serum on mixing the two sera. 

 As Tchistovitch noted, these precipitates are soluble in small 

 amounts of alkali (potassium, sodium or ammonia), as we also found 

 to be the case with our rabbit serum specific for hen blood. 



It would seem reasonable that these phenomena are similar to 

 those which Kraus noted. The specific serum from animals injected 

 with blood serum from another animal causes an opacity in the 

 serum of the species used for inoculation. Serum from animals in- 

 jected with bacterial cultures causes an opacity in the culture fluid 

 in wmich the organism used for vaccination has grown. The pre- 

 cipitate that we have mentioned bears the same relation to Kraus' 



