2050 Journal of Applied Microscopy 



small drop should now be placed on the small ruled space of the counting 

 chamber. Apply the cover immediately to insure accurate results. If too large 

 a drop is used it may get between the cover and the outer supporting cell. If 

 the drop is too small the ruled space may not be filled properly. In either case, 

 clean the chamber and cover and try again. Set aside to settle. The pipette 

 should be cleaned at once to prevent coagulation of the blood in the capillary 

 tube. Blow out the blood solution in it. Draw it part full of distilled water, 

 blow this out, then use alcohol and finally ether in the same way. 



For counting the prepared slide an objective of the same power as the 

 Bausch & Lomb one-fifth should be used. Count the cells in the squares, begin- 

 ning at the upper left corner. Count all of the cells on the upper line, the line to 

 the left as well as those in the square. Cells on the lower line and the line to the 

 right will be counted with the next line of squares. The cells in 100 squares 

 should be counted to arrive at accurate results. To compute the number of red 

 cells per cubic millimeter divide the number of cells by the number of squares 

 counted, the result will be the average number of cells in one square. Multiply 

 this by 4000 as each square is 1-400U of a cb. mm. Multiply this result by 100 

 as the blood has been diluted 100 times. For example, suppose lOli squares are 

 counted, the number of cells being 1200 — 1200 : 100=12.0, the number of 

 cells per square. 12.0 4000 = 50,40(1 :< lOd, the dilution ^ 5,(»40,0(M), the 

 number of cells per cubic millimeter. 



To count the white corpuscles proceed in the same way except that blood 

 should be drawn into the pipette marked 1 and 11, to the 1 mark, followed by the 

 dilutent, which should be a one-half per cent, solution of acetic acid in distilled 

 water, to the mark 11. Thoroughly mix and put a drop in the counting chamber 

 and proceed as in counting red cells. The acid solution will destroy the red 

 corpuscles and render the white corpuscles more distinct. The computation of 

 the white corpuscles in one cb. mm. of blood is the same as for red except that 

 last multiplication should be by 10, as the dilution is but It* times. 



The centrifuge method of estimating the quantity of plasma and red cells is 

 sufficiently accurate for general purposes. Examinations may be made from 

 fresh blood and from diluted blood which may be conveyed a distance, the exam- 

 inations being made some hours later. 



Centrifuge Percentage Tube. Twice actual size. 



To examine fresh blood, clean a finger with soap and water, alcohol and 

 ether. Dry thoroughly. Puncture with a blood lancet and fill one of the per- 

 centage tubes. A large drop of blood is required. The tube will fill automati- 

 cally if the opposite end to the one in the blood is depressed. Insert the tube 

 in the haematokrit and revolve immediately for three minutes at a speed of from 

 eight to ten thousand revolutions per minute. Multiply the number of divisions 

 filled with red corpuscles by 100,000. The result will be the number of red 

 corpuscles per cubic millimeter of blood. When it is necessary to carry the 

 blood from the patient to the office, proceed as follows to dilute and preserve the 

 blood. Draw blood into a capillary tube to a certain height, and b!ow it into a 

 small clean vial in which an equal amount of a 2.5 per cent, solution of potas- 

 sium bichromate in water has been previously measured and placed. Mix 

 thoroughly. Fill a percentage tube with this mixture and revolve the same as 

 fresh blood. Multiply the number of spaces filled by 100,000 and then by two 

 on account of the dilution. William H. Knap. 



Harvey Medical College. 



