BLOOD. 



213 



in position, is exactly o.i millimeter deep. The floor of the cell 

 is divided by delicate lines into squares each of which is /4oo of a 

 square millimeter in area (see Fig. 72, page 215). The volume of 

 blood therefore between any particular square and the cover-glass 

 above must be Yiooo cubic millimeter. Accompanying each instru- 



FIG. 70. 



THOMA-ZEISS COUNTING CHAMBER. (Da Costa.) 



ment are two capillary pipettes (Fig. 71, page 2 14), each constructed 

 with a mixing bulb in its upper portion. Each bulb is further pro- 

 vided with an enclosed glass bead which is of great assistance in 

 mixing the contents of the chamber. The stem of each pipette is 

 graduated in tenths from the tip to the bulb. The final graduation 

 at the upper end of the bulb is 101 on the pipette used in mixing the 

 blood sample in which the erythrocytes are counted (erythrocy- 

 tometer, see Fig. 71, page 214), and n on the pipette used in mix- 

 ing the blood sample for the leucocyte count (leucocytometer, see 

 Fig. 71, page 214). In making " blood counts" with the hsemo- 

 cytometer it is necessary to use some diluting fluid. Two very 

 satisfactory forms of fluid for this purpose are Toison's and Sher- 

 rington's solutions. 1 When either of these solutions is used as the 

 diluting fluid it is possible to make a very satisfactory count of 

 both the erythrocytes and leucocytes from the same preparation, 

 since the leucocytes are stained by the methyl-violet or methylene- 

 blue. 



In counting the erythrocytes by means of the haemocytometer, 

 proceed as follows : Thoroughly cleanse the tip of the finger or 



Poison's solution has the follow- 

 ing formula: 



Methyl violet 0.025 gram. 



Sodium chloride I gram. 



Sodium sulphate 8 grams. 



Glycerol 30 grams. 



Distilled water 160 grams. 



Sherrington's solution has the fol- 

 lowing formula : 



Methylene-blue o.i gram. 



Sodium chloride 1.2 gram. 



Neutral potassium ox- 



alate 1.2 gram. 



Distilled water 300.0 grams. 



