450 MICROBIOLOGY 



serum of rabbits treated with the serum of chickens gave a 

 specific precipitate when mixed with chicken serum. This in- 

 vestigation has been extended to other substances. Wasser- 

 man 17 produced an antibody which precipitated the casein of 

 the particular variety of milk employed for immunization. 



The precipitins, like the agglutinins, are inactivated by 

 heating from 60 to 70 C. and they are not reactivated by the 

 addition of normal serum. 



The precipitins are supposed to be specific. They are 

 being used quite extensively for the differentiation of animal 

 proteids. Precipitation, as with agglutination, brought about 

 by bacterial stimulation, has to a certain extent, "group" 

 reaction. 



Opsonins. Denys and Leclef 1S called attention to the 

 fact that blood serum aided phagocytosis by its action upon the 

 bacteria rather than upon the leucocytes. They procured ex- 

 perimental evidence that substances which alter bacteria in 



"If test tubes are employed, they are best observed by tilting 

 them and looking through a thin layer of the contained fluid at a 

 dark surface or at the sky. In either case the flocculent collections 

 of agglutinated bacteria can be seen. 



"The test can also be made and observed under the microscope 

 by the hanging-drop method, but in working with such small quanti- 

 ties much of the accuracy of the technic is apt to be lost. 



"Some knowledge is required in order to form correct deduc- 

 tions from the experiments. Thus, with typhoid blood, the aggluti- 

 nation of the typhoid bacillus usually occurs within an hour in dilu- 

 tions of 1:50, but the agglutinability of the culture employed should 

 be known before the experiment is undertaken. 



"Similarly, when the method is employed for the differential 

 treatment of bacteria, the value of the serum should be known at 

 least approximately." 



For a detailed method for the agglutination test for the diag- 

 nosis of glanders, see B. mallei. It will be noted that there are two 

 distinct methods for observing the agglutination for diagnosis (1) 

 macroscopic and (2) microscopic. 



17 Wasserman. Deut. med. Woch., Bd. XXIX (1900). 



18 Denys and Leclef. La cellule, Vol. XI (1895) p. 198. 



