OPSONINS, AGGLUTININS, PRECIPITINS, LYSINS 139 



Precipitins. Shortly after the discovery of the agglutinins it 

 was shown that immune serum when mixed with the germ-free 

 filtrate of a culture of the corresponding organism produced a 

 cloudiness and afterwards a precipitate. Several authorities con- 

 sider the precipitins and agglutinins are identical. It is reason- 

 able to assume that in an old broth culture the bacteria undergo 

 disintegration and pass into solution. Accordingly the substances 

 which when in the bacterial body are agglutinated may, when in 

 solution in the bacteria-free filtrate, be precipitated. The test is 

 made in the same way as the macroscopic test described for agglu- 

 tinins, except that the filtrate of a culture is used instead of a bac- 

 terial suspension. 



It has been found that precipitins may be produced by injecting 

 albuminous substances into suitable animals. Thus a rabbit im- 

 munized to human serum will produce a precipitate when mixed 

 with human serum ; similarly a rabbit immunized to horse serum 

 will produce a precipitate when mixed with horse serum. This 

 fact has found a practical application in forensic medicine ; blood 

 spots dissolved out in normal salt solution can be recognized as 

 of human or animal origin even after months of drying. The test 

 is also used in determining the nature of meat suspected to be horse 

 flesh. 



Lysins. The bacteriolysins were discovered by Pfeiffer in 

 his attempt to immunize animals against cholera by the injection 

 of live cultures. It was soon discovered that the lytic action 

 Pfeiffer had noticed, the so-called Pfeiffer's phenomenon, would 

 take place not only in the peritoneal cavity of a guinea pig but 

 also in a test tube when the immune serum of the animal was at 

 once mixed with its antigen. According to Ehrlich this disinte- 

 gration of bacteria occurs as a result of their union with an anti- 

 body and complement. To the antibody he gave the name of 

 amboceptor because he considered it as an interbody linking to- 

 gether the antigen and complement. One of the extraordinary 

 facts connected with the reaction is that the active part of the 

 combination, the complement, is normally present in the blood, 

 but only when united with a specific amboceptor can it affect the 



