176 MICROMETRY AND BLOOD PREPARATIONS 



count corpuscles in the adjoining sixteen squares. Put down this count. Then in 

 third sixteen squares. Put down the number. Now move down to next row of 

 three triple-ruled squares. Count the number of corpuscles in each of the three 

 sixteen-square spaces and set down the numbers for addition. We have now counted 

 ninety-six small squares (6X 16). Count at any place four additional small squares 

 and add number of blood-cells contained therein to those in the ninety-six small 

 squares already counted. Divide the sum by 100 or simply point off two decimals. 

 This gives the average for each small square. Multiply this by the dilution and then 

 (as the small square is only 1/4000 cu. mm.) by 4000. This will give the number of 

 corpuscles in i cubic millimeter. Example: 100 small squares contained 655 red 

 cells. Pointing off, 6.55 equals average number of red cells per small square. 

 Multiply by dilution (200) and then by 4000 (the small square is 4000 times smaller 

 than the unit: i cu. mm.) 6.55X200=1310X4000 = 5,240,000. 



At least 100 small squares, and preferably 200 should be counted. 

 If the blood appears normal, one may simply count the number of red 

 cells in five of the sixteen small square spaces (eighty small squares). 

 Having added the numbers and multiplying by 10,000, you obtain the 

 number of cells in i cubic millimeter. (Eighty small squares is 1/50 of 

 the unit of i cu. mm., or 4000 small squares. The blood dilution being 

 i to 200, we have 50 X 200 X number of cells in eighty small squares.) 



In counting, count corpuscles lying on the lires above and to the right. Do not 

 count those lying on lines below and to the left. 



In the small squares count only corpuscles lying in the space or cutting the upper 

 line. This prevents counting the same cell twice. 



To Count White Cells. Draw up the fluid in the white pipette to 

 the mark 0.5. Then, still holding the pipette as near the horizontal as 

 possible, because the column of blood tends to fall down in the larger 

 bore, draw up by suction a diluting fluid which will disintegrate the red 

 cells without injuring the whites. The best fluid is 0.3 % of glacial acetic 

 acid in water. This makes the white cells stand out as highly refractile 

 bodies. Some prefer to tinge the fluid with gentian violet. The 0.5 

 mark is preferred because it takes a very large drop of blood to fill the 

 tube up to the i mark and if there is much of a leukocytosis a i to 10 

 dilution is not sufficient. In leukaemic blood it is better to use the red 

 pipette with the 0.3% acetic acid solution. 



The blood having been drawn up to 0.5, we have a dilution of i to 20. 

 Making a preparation, exactly as was done in the case of the red count, 

 we count all of the white cells in one of the large squares (i sq. mm.). 

 The cross ruling greatly facilitates this. Note the number. Then 

 count a second and a third large square. Strike an average for the large 

 squares counted and multiply this by 10, as the depth of the fluid gives 



