QUANTITATIVE ESTIMATION OF BACTERIOTROPINS 203 



13. In opsonic work the question as to how a certain element ought 

 to be counted becomes quite evident and important. The proper 

 method of procedure is to determine definitely how they may best be 

 dealt with, and then to follow the rule adopted consistently. If an 

 organism rests on the border of a cell, it will be better to consider it as 

 within the cell and count it. Diplococci or division forms may be 

 counted as one or as two, provided we are consistent in our method. In- 

 dividual organisms, as distinguished from zoogleic masses, which may 

 be lying on the top of the cell, are counted as if they were within the 

 cell; for we have no means of determining definitely whether or not our 

 suspicions are well grounded. In the case of a beaded or vacuolated 

 bacillus, it is always better to count the whole element as a unit. 



14. The phagocytic index is the average number of bacteria or other 

 cells ingested per leukocyte after counting at least from 50 to 100 cells. 

 The total number of bacteria ingested is divided by the total number of 

 phagocytes, the result being the average number of bacteria ingested 

 per leukocyte i. e., the phagocytic index. 



15. The opsonic index is then given by the ratio 



Patient's phagocytic index 

 Control phagocytic index 



For example, with patient's serum, 100 phagocytes contain 300 bac- 

 teria, the phagocytic index being -f--- = 3. With the control serum, 100 

 phagocytes contain 500 bacteria, the phagocytic index being fw = 5. 

 The opsonic index is : 



3 Patient's phagocytic index _/\/ 

 5 Control phagocytic index 



16. Simon and Lamar have suggested a modification of Wright's 

 method that has been adopted by many laboratories. It consists in 

 diluting the patient's and control serums up to 1 : 10 or 1 : 100, and pre- 

 paring mixtures of various dilutions with leukocytes and thinner bac- 

 terial emulsions. The percentage of phagocytic cells in the mixtures 

 containing the serum to be tested is compared with the mixtures con- 

 taining normal serum. It is, therefore, a method of comparative phago- 

 cytic indices. 



QUANTITATIVE ESTIMATION OF BACTERIOTROPINS (NEUFELD) 

 Of the various methods for standardizing an immune serum, par- 

 ticularly antimeningococcus serum, and of obtaining some idea of its 



