THE MEIOSTAGMIN KEACTION 193 



a rabbit three to five intravenous injections at intervals of seven 

 days of killed culture of a virulent strain of the organism, e.g. 

 typhoid or cholera. The culture is killed by heating to 60-65 C. 

 for half an hour, and the dose is increased from one loop to ten 

 loops of an agar culture. Seven days after the last dose the animal 

 is bled from an ear vein, and the serum obtained. The agglutinating 

 value of the serum must be determined, and controls should always 

 be put up with normal serum of an animal of the same species as 

 that from which the immune serum has been obtained. A series of 

 dilutions of both sera is made with salt solution and a twenty-four 

 hour agar culture of the organism to be tested used. Both the 

 macroscopic and microscopic methods should be employed. The 

 dilutions may be made with a 1 c.c. pipette graduated in hundredths, 

 with the haemocytometer pipettes, or by the method used clinically. 



2. Saturation test. Castellani noticed that a suspension of a 

 microbe added to the homologous agglutinating serum absorbs 

 most, if not all, the specific agglutinin, whereas an organism not 

 homo]ogous with the serum absorbs little or only a portion of the 

 agglutinin. The test may be carried out as follows : 



Ten loopfuls of a young agar culture of the organism to be tested 

 are mixed with 10 c.c. of a 5 per cent, solution of a highly aggluti- 

 nating serum. After incubating for two or three hours, the mix- 

 ture is centrifuged, the clear supernatant fluid decanted, and 

 the agglutinating power of the decanted liquid is then tested on the 

 organism with which the serum was prepared. If the organism 

 tested is homologous with the organism with which the agglutinat- 

 ing serum was prepared, the decanted fluid will have lost most, 

 or a considerable proportion, of its agglutinating power for the 

 latter. 



THE MEIOSTAGMIN REACTION. Ascoli has found that if an 

 immune serum be mixed with an alcoholic extract of the homologous 

 antigen and the mixture incubated at 37 C. for two hours the 

 surface tension is reduced ; if the serum and antigen extract are 

 not homologous the surface tension is unaltered. For example, in 

 the case of typhoid the following is the procedure. An alcoholic 

 extract of typhoid bacilli is prepared ; this is diluted with saline 

 solution to 1-1000 1-1,000,000. The typhoid serum is similarly 

 diluted, 1-10. To 9 c.c. of the diluted serum 1 c.c. of the diluted 

 antigen extract is added. By means of some form of viscosimeter 

 or stalagmometer the number of drops yielded by a given volume 

 of the mixture is ascertained, immediately after the mixture is 

 made and after the mixture has been incubated at 37 C. for two 

 hours. If the surface tension has been reduced, the number of 



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