392 EXPERIMENTAL INFECTIONS DURING LIFE 



Transfer to the third trough containing distilled 

 water, and holding the trough over a sink, run in a 

 stream of distilled water until washing is complete. 

 Remove slides from the rack and dry. 



Leishman's stain is the best for routine work for all 

 bacteria other than B. tuberculosis. Films containing 

 tubercle bacilli must of course be stained by the Ziehl 

 Neelsen method. 



FIG. 196. Glass staining trough for blood films. 



1 3 . Examine specific serum slide microscopically with 

 i/ 12 inch oil immersion. Find the edge of the blood 

 film along this the bulk of the leucocytes will be 

 collected. Starting at one end of the film move the 

 slide slowly across the microscope stage and as each 

 leucocyte comes into view count and record the number 

 of ingested bacteria. The sum of the contents of the 

 first 50 consecutive polymorphonuclears that are en- 

 countered is marked down. (The average number of 

 bacilli ingested per leucocyte = the " phagocytic index.") 



14. In precisely similar manner enumerate the bac- 

 teria present in the first 50 cells of the control prepa- 

 ration. This number is recorded as the denominator 



