228 CLINICAL BACTERIOLOGY AND HiEMATOLOGY 



2a. Eosinophile myelocytes (Plate VII., Fig. 12) do not occur in 

 healthy blood, and bear the same relation to the eosinophile cells 

 as ordinary myelocytes to the polynuclear cells. They are dis- 

 tinguished from eosinophils by their larger size and relatively 

 large circular nucleus. 



3. Basophile Cells or Mast Cells (Plate VII., Fig. 9).— These are 

 about as large as polynuclears, and have twisted (usually trilobed) 

 nuclei, which occupy more of the cell than do those of the poly- 

 nuclears. They have a comparatively small number of granules, 

 which (unlike those of the other leucocytes) vary in size and stain 

 blue or purplish-blue with Jenner. The granules do not stain at 

 all with triacid. 



They are often not found in persons in robust health, but in the 

 average hospital patient occur in small numbers — usually less 

 than ^ per cent. 



3a. Large Mast Cells (Plate VII., Fig. 13). — These occur only in 

 the blood in myeloid leucocythsemia, and are very characteristic 

 of that condition. They may possibly be eosinophile myelocytes 

 with degenerated granules. 



Method of making a Differential Count. 



Having prepared a film by any of the methods previously 

 described, the next step is to make a differential count in the 

 following way : Focus the film under the microscope, using an 

 oil-immersion lens ; when you have had sufficient experience it 

 is quite easy to make the count with a ^-inch lens, which is 

 quicker, but not advisable for beginners. Then note down the 

 nature of each leucocyte as you come to it, moving the film 

 across the stage of the microscope from end to end, and then 

 moving it a little way upwards or downwards and returning in 

 the opposite direction, so as never to pass over the same part of 

 the film twice. The simplest way of noting down the leucocytes 

 is to assign single letters to each variety, P for polynuclear, E for 

 eosinophile, etc., and to put these down in blocks of five each way, 

 thus : P P P L E 



P P L L H 



L P PP P 



P L L P L 



P P P L P 



In this way you can tell at any time how many leucocytes you 

 have counted. It is much quicker to dictate the numbers to a 



