PREPARATION OF VACCINES 219 



corpuscles are well mixed. The 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 

 fine 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 containing 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 T 7 ^ 5 - = 0-6, i.e. not much 

 more than half the normal. 



Preparation of vaccines for treatment, etc. The vaccine used for 

 treatment is a sterilised, standardised suspension of the infecting 

 organism, except in the case of tuberculosis, for which tuberculin 

 (TR 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. 



The vaccine is prepared by growing the organism under appro- 

 priate conditions, , the staphylococcus on agar, the streptococcus, 



