SERUM DIAGNOSIS 169 



prepared or sensitized bacteria are ingested by 

 the leukocytes. 



At the end of the second incubation, the tubes 

 are removed from the water bath, the superna- 

 tant fluid decanted and, by means of a sterile 

 platinum loop, a quantity of the sediment con- 

 sisting of bacteria and leukocytes is removed 

 from each of the tubes which contained the 

 serum to be tested, as well as from the tubes con- 

 taining the control normal serum; and smears 

 from the sediments are made on microscopic 

 slides. These smears are fixed and stained in 

 the usual way and are then examined under the 

 microscope, and the bacteria in 100 polymor- 

 phonuclear leukocytes are counted in each of the 

 stained smears. The average number of bac- 

 teria taken up per leukocyte from the serum be- 

 ing tested, divided by the average number of 

 bacteria per leukocyte from the normal serum is 

 the "opsonic index." 



PRACTICAL VALUE OF THE OPSONIC INDEX 



Little of the diagnostic value which was ex- 

 pected of the opsonic test has been realized. An 

 immense amount of investigation has revealed 

 the fact that the opsonic index cannot be ob- 



