264 CLINICAL BACTERIOLOGY AND PLEMATOLOGY 



2. Eosinophile Leucocytes (Plate VII., Fig. 8). These are 

 about as large as a polynuclear, and have a nucleus which is 

 usually bilobed, but which may be more distorted. The chief 

 feature of the cell is the presence of numerous relatively large 

 granules which stain brilliantly with the eosin; they are 

 spherical in shape and very uniform in size. They average 

 about i to 4 per cent, of the leucocytes in health, but slightly 

 higher or lower figures may occur. 



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 distinguished from eosinophiles 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 mojre of the cell than 

 do those of the polynuclears. 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 of robust health, but 

 in the average hospital patient occur in small numbers 

 usually less than J per cent. 



3. 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 experi- 

 ence it is quite easy to make the count with a J-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, 



