RED CELL COUNTS 



203 



faces. The blood is run in by capillarity from the mixing pipette. I gave up this 

 type of counter because the clamps made manipulation awkward and because the 

 usual apparatus is most satisfactory. 



Red Cell Counts. To make a red count: Having a fairly large drop of blood, ap- 

 ply the tip of the 101 pipette to it and, holding the pipette horizontally, carefully 

 and slowly draw up with suction on the rubber tube a column of blood to exactly 

 0.5 or i. The variation of ^ 5 inch from the mark would make a difference of al- 

 most 3%. If the column goes above 0.5, it can be gently tapped down on a piece 

 of filter-paper until the 0.5 line is cut. Now insert the tip of the pipette into some 

 diluting fluid and, revolving the pipette on its long axis while filling it by suction, 

 you continue until the mark 101 is reached. A variation of ^ 5 inch at this mark 

 would only give an error of about one- thirtieth of i%. After mixing thoroughly by 

 shaking for one or two minutes, the fluid in the pipette below the bulb is expelled 

 (this, of course, is only diluting fluid). A drop of the diluted blood of a size just 

 sufficient to cover the disc when the cover-glass is adjusted, is then deposited on the 

 disc and the cover-glass applied by a sort of sliding movement, best obtained by using 

 a forceps in one hand assisted by the thumb and index-finger of the other. 



Among diluting fluids Toisson's is probably the best: 



Sodium chloride i gram 



Sodium sulphate 8 grams 



Glycerine 30 c.c. 



Distilled water 160 c.c. 



Dissolve the sodium chloride and the sodium sulphate in the glycerine water and 

 add sufficient methyl or gentian violet to give a rich violet tint. 



Hayem's solution is very satisfactory and is preferred by many workers. It has 

 the following composition: Corrosive sublimate 0.5 gram, Sod. chloride i gram, 

 Sod. sulphate 5 gram, 200 c.c. of distilled water. 



A 2^% solution of potassium bichromate makes a very satisfactory diluting 

 fluid in the counting of red cells. 



A salt solution of about i% strength, tinged with about i drop of a saturated 

 alcoholic solution of gentian violet to about 50 c.c., is a good substitute, or the salt 

 solution alone will answer when no white count is to be made at the same time as the 

 red one. 



It is important to work quickly in adjusting the cover-glass, or there will be cells 

 settling in the center of the drop from a greater depth than the one which the apposi- 

 tion of the cover-glass makes (Ko mm - deep). 



A good preparation should show: 



1. Presence of Newton's rings. 



2. Absence of air bubbles. 



3. Entire surface of ruled disc covered. 



4. Equal distribution of cells. 



Before counting, about five minutes should be allowed for the set- 

 tling of the cells. 

 It will be remembered that the small squares are ^o mm. square. The 



