JLEMACYTOMETER. 149 



4. Expel the fluid that fills the stem and wipe the point. 



5. Blow a small drop of the diluted blood on to the central 



platform of the counting chamber, and apply the cover. 

 On pressing the latter down 



6. Newton's rings should be seen between the rim of the cell 



and the cover. 



7. Let the preparation rest for two minutes, the blood cells 



settle on the floor of the chamber. 



8. Count the cells in at least 16 squares. Cells astride the 



lines are to be counted on two sides of each square only. 



Calculation : 



Number of cells (200 ?) x 4000 x 100 R.B.C. in 1 cubic milli- 

 Number of squares (16 ?) metre of blood. 



Oliver's Hsemaeytometep (used in the darkened room). 



(1) A graduated flattened tube, (2) an automatic blood measurer to 

 which (3) a mixing pipette is adjustable for washing it out, (4) a candle 

 (Christmas candle), (5) a bottle of Hayem's solution (see pg. 61). 



Process: (1) Dry the measurer by drawing darning thread through it 

 with a needle. (2) Prick your finger and fill the measurer by 

 touching the drop of blood. (3) Attach the mixer, filled with 

 Hayem's fluid, to the measurer by means of the rubber tube and 

 wash the blood thoroughly into the graduated tube. (4) Mix 

 thoroughly by inverting three times. In withdrawing the thumb 

 draw it against the edge to avoid loss of fluid. (5) Place the 

 lighted candle ten feet off. (6) Grasp the tube by the flat sides 

 framing it between the thumb and fore-finger, hold it close to the 

 eye, and look through its long diameter at the flame. (7) Add 

 small quantities of Hayem's fluid, repeating (4) until the eye can 

 distinguish the first appearance of a transverse line of light. (8) Head 

 the graduation touched by the upper edge of the column of mixture 

 and calculate as follows : 100 degrees correspond to the assumed 

 normal of 5,000,000 cells per cubic millimetre. Each degree above 

 or below tViis indicates 50,000 cells above or below the normal. 

 The W. B.C. in a state of health do not affect the readings. 

 This instrument has been standardised by means of the Thoma- 



Zeiss instrument. 



