THE TECHNIQUE OF SERUM REACTIONS 257 



ing motion. A column of peritoneal flmd will run into the glass tubing 

 by capillary attraction; this can then be blown out upon a cover-slip 

 for hanging-drop examination or may be blown upon a slide, smeared, 

 and examined after staining. The reaction is regarded as positive if 

 within thirty minutes to an hour the peritoneal exudates of the animals 

 receiving immune sera contain only swollen or disintegrated microor- 

 ganisms, while in that of the control animals only well-preserved and 

 undegenerated bacteria are found. In dealing with typhoid bacilli 

 and cholera spirilla, in connection with which the test is most often 

 used, active motility in the controls is of much help. Should there be 

 extensive degeneration of the bacteria in the exudate of the control 

 animals the test is of no value. 



2. Identification of a microorganism by observing its a susceptibility to 

 lysis in a known immune serum in vivo: 



The technique for this test is practically the same as that of the 

 preceding except that in this case we require a potent known immune 

 serum and normal serum for control. It is necessary, furthermore, that 

 by previous tests we should know the degree of dilution in which the 

 immune serum will cause complete bacteriolysis of the microorganism 

 used in its production. Thus, if we are employing a typhoid immune 

 serum and are about to test by this method an unknown Gram-negative 

 bacillus, we must know the titer of the serum for the typhoid bacillus 

 itself. 



Mixtures are then made of dilutions of this serum and definite 

 quantities of the microorganism to be tested. It is best, always, to 

 employ from ten to one hundred times the amount of immune serum 

 which suffices to produce lysis with its homologous microorganism. 

 Thus, if the serum has been found to be active in dilutions of 1 : 1,000, it 

 is employed in the test in dilutions of 1 : 1,000, 1 : 100, and 1 : 10. These 

 dilutions are then injected into guinea-pigs in quantities .of 1 c.c. together 

 with the bacteria to be tested, and control gxiinea-pigs are injected with 

 undiluted normal serum mixed with the bacteria and with salt solution 

 and the bacteria. The exudates are then observed in the same way as 

 in the preceding experiment. 



Bactericidal Reactions in the Test Tube. — Bactericidal reactions 

 in the test tubes may be made by mixing in small sterile test tubes, 

 definite quantities of the bacteria with inactivated serum and com- 

 plement, the latter in the form of unheated normal serum. The 

 mixtures, diluted with equal volumes of neutral broth or salt sdution, 

 are set away for a definite time three to four hours in an incubator at 



