104 ANTIBODIES AND OPSONINS. 



These substances are called haemolysins. The discovery of the 

 presence of antibodies and their mode of action under certain 

 fixed conditions have been considerably used in bacteriology 

 and to a less degree in medical jurisprudence. A brief de- 

 scription of their mode of application will be made. 



Agglutination Demonstration. For this is required a suit- 

 able dilution of serurn and a suitable emulsion of a young 

 culture of the bacteria to be tested. The Gruber-Widal reac- 

 tion, which will be described under the heading of B. typho- 

 sus, is a classical example of agglutination reaction. 



Precipitin Demonstration. An animal, preferably a rabbit, 

 is injected at intervals of about six days, until four or five in- 

 jections have been given, with the material (bacterial or pro- 

 teid) for which it is desired to produce a precipitin. About 

 a week or more after the last injection blood should be drawn, 

 with all precautions necessary against contamination, and a 

 clear serum obtained and preserved in a cool, dark place. 

 Any cloudiness developing should be removed by means of a 

 Berkefeld filter. Salt solution emulsion of bacteria grown 

 for ten days on agar, or a solution of the proteid, if such is 

 being tested, in salt solution, is filtered until a clear solution 

 results. In the actual test a small fixed quantity, usually 

 about 0.5 c.c. of serum to be tested, is mixed in a small test- 

 tube with about 1 c.c. of bacterial filtrate or proteid filtrate. 

 Usually controls of normal serum and plain salt solution, a 

 plain salt solution and filtrate, or both are made at the same 

 time. Some authors recommend that in proteid tests 0.1 c.c. 

 of serum and 2 c.c. of filtrate be used. When the tubes are 

 prepared as described above they are placed for one hour in 

 an incubator at 37.5 C. If the specific precipitin is present, 

 there will be formed a distinct haziness or even a flocculent 

 precipitate. 



Lysins may be demonstrated either by test-tube tests (In 

 vitro) or by testing the substances in the peritoneal cavity of 

 some animal (in vivo), a guinea-pig being generally used. 

 The latter test is the well-known Pfeiffer's phenomenon. It 

 depends on the fact that bacteria mixed with a homologous 

 immune serum undergo solution when injected into the peri- 



