298 PRECIPITINS 



ity, and they are of value chiefly as indicators of this general antibody 

 formation. They may, however, be concerned in preparing their anti- 

 gens for destruction and solution, just as opsonins prepare cells for pha- 

 gocytosis, but precipitins themselves possess no appreciable curative or 

 protective virtues, and are of value chiefly in diagnostic procedures. 



PRACTICAL APPLICATIONS 

 BACTERIAL PRECIPITINS 



Bacterial precipitins have no clinical diagnostic value. Their re- 

 actions have no advantage over the agglutination test, they are more 

 difficult of execution than the latter, the sources of error are greater. 



In scientific research they may be of value in differentiating micro- 

 organisms from closely allied species, but even here agglutination 

 reactions serve the purpose equally well and are less difficult of 

 execution. 



Occasionally bacterial precipitins are of service in demonstrating 

 the presence of soluble bacterial substances within exudates or organic 

 fluids. For example, Vincent and Bellot recommend the reaction as 

 being of considerable value in the diagnosis of cerebrospinal meningitis. 

 The cerebrospinal fluid is centrifugalized until it is clear; 2 c.c. of this 

 clear fluid is then placed in one tube and 4 c.c. into another. One-tenth 

 cubic centimeter of a standard antimeningococcic serum is added to 

 each tube. The tubes are kept for from twelve to fifteen hours at 37 C. 

 In the presence of cerebrospinal meningitis a precipitate forms. If the 

 fluid is normal or if it was derived from some other form of meningitis, 

 no cloudiness results. This reaction is said to occur within the first 

 twenty-four hours of the illness and to persist until the twelfth to the 

 twentieth day. 



Similar reactions have been advocated in the diagnosis of other in- 

 fections, particularly syphilis. Fornet believed that the presence of 

 typhoid antigen (precipitinogen) ought to be capable of demonstration 

 in the blood-serum of typhoid fever patients long before antibodies 

 themselves are in evidence. One cubic centimeter of potent immune 

 serum in concentrated and diluted form (1:5 and 1: 10 with normal salt 

 solution) is placed into small test-tubes, and an equal amount of the 

 serum for examination, also in concentrated and similar dilutions, is 

 carefully floated on top of the immune serum. Control tests with nor- 

 mal and immune serum and normal with unknown serum are made. 

 The mixtures are allowed to stand undisturbed at room temperature for 



