AGGLUTINATION. 105 



broken off ; thus two pieces 1 cm. long and filled with 

 clear serum are obtained. 



2. Collection of serum from animals. A rabbit is injected 

 with cultures of typhoid or cholera, devitalized by heat, 

 following the detailed directions given in connection with 

 typhoid and cholera. After about ten days the animal is 

 bled from the carotid and the serum separated by standing 

 in a tall cylinder in a cool place or by centrifugation. 

 The measurement of the serum and the diluting fluid is 

 carried out by means of uniformly wide capillary tubes, 

 which are marked off with ink-lines in lengths of a centi- 

 meter each. The relative and not the absolute quantities 

 of the materials are thus known. In the following, when 

 I speak of 1 cm. of serum, I mean that contained in a 

 piece of a capillary tube 1 cm. long. 



The bacteria are always employed as a suspension in 0.5 

 c.c. of bouillon, one loopful ^ (2 mg. ) of a twenty -four 

 hours' agar culture (37°) being used in its preparation. 



The serum is also diluted with bouillon. 



For demonstrating the injurious action upon bacteria, 

 we have two methods : The demonstration of the specific 

 agglutinating material according to Gruber and Durham, 

 and the specific bactericidal material according to R. Pfeif- 

 fer. 



1. Demonstration of agglutinin, ^ after Gruber and Durham 

 (Munch, med. Wochenschr. _, 1896, 206 and 285). If it 

 is desired to make a macroscopic demonstration (little used), 

 0. 6 c. c. of the suspension of the bacteria is added to 0. 5 c. c. 

 of serum diluted fifty times, and it is noted in a very nar- 

 row test-tube whether there occurs a visible clumping of the 

 l)acteria with clearing up of the fluid. If after ten to fifteen 

 minutes, or at most one hour, no reaction occurs in the in- 

 cubator, the serum in a dilution of 1 : 50 is not active uijon 

 the variety of bacteria tested, and we may repeat the test 

 with stronger concentrations. On the contrary, the ex- 



1 The loopful is estimated by weighing the empty and full loop on 

 the needle. 



' If one employs more bacteria, the action of the serum is weaker. 

 In order to obtain cultures that are readily broken up, the culture is 

 prepared upon agar that has been somewhat dried by being previously 

 kept in the incubator for twenty-four hours. 



