OPSONIC DETERMINATIONS 263 



various mixtures washed corpuscles, bacterial suspension, and 

 serum are made and incubated as previously described. In 

 order to make the film for staining and counting, the contents of 

 the pipette are discharged on to one end of a slide roughed with 

 finest emery paper, and the mixture is spread by means of a slide 

 which has been broken across after notching with a file or glass 

 cutter. The object is to obtain a broken edge having a very 

 slight concavity, and many slides may have to be sacrificed to 

 attain this. The film is spread by drawing (not pushing) along ; 

 the leucocytes adhere to the edge of the spreader, and finally are 

 deposited mostly at the end of the preparation, the red corpuscles 

 being left behind. 



Lastly, the films after staining are examined with the oil- 

 immersion lens, preferably with the aid of a mechanical stage, 

 and the number of organisms contained in not less than fifty 

 polymorphonuclear leucocytes is counted. Parts of the film in 

 which the cells are broken down or not well stained, or cells con- 

 taining obvious clumps of organisms, should be avoided. The 

 ratio between the number in the control and the number in the 

 specimen prepared with the patient's serum gives the opsonic 

 index. Thus, if in the control there are 125, while in the patient's 

 specimen there are 75, the index would be ^^ = 0-6, i.e. not much 

 more than half the normal. 



Determinations of the opsonic index are now not often made. 

 The method is laborious and requires much practice to obtain 

 results of any value, and many assert that the liability to error 

 is so great that results are unreliable. It may be said, however, 

 that with careful technique and in practised hands information 

 has been acquired which has been of the greatest value in vaccine 

 treatment. 



Preparation of Therapeutic Vaccines 



The vaccine used for treatment is a sterilised, standardised 

 suspension of the infecting organism, except in the case of 

 tuberculosis, for which tuberculin (TK or BE) or an analogous 

 preparation is employed. In certain instances a mixture of 

 organisms is used e.g. M. pyogenes, var. aureus and var. albus, 

 with or without the acne bacillus in some cases of acne and 

 the strain of organism isolated from the lesion is generally to be 

 preferred. 



