136 SPECIAL PHYSIOLOGY 



Roll the pipette as before when filled and in a few moments the 

 mixture will turn quite dark; when it no longer changes color it is 

 ready to be counted. Allow a few drops to flow out of the tube as 

 in the case of the red-cell pipette, then place a small drop from the 

 end of the pipette on the ruled plate. It is not necessary to blow 

 the fluid out; it will run out. Take the same precautions in filling the 

 counter and adjusting the cover-glass as before, except that there is 

 no need of haste in placing the cover-glass, because the white cells are 

 lighter. 



Here, because we have a clear field with little in it, and the cells 

 are quite large, we can use a lower power of the microscope and see 

 a whole square millimetre at once. Begin at the upper left-hand 

 corner and count the cells in each space 1 mm. square, and observe 

 the same method in keeping the record as when counting the red cells. 

 Clean the counting slide, roll the pipette for a moment, and refill 

 the marked plate and count the nine spaces again, keeping the 

 records as before. Do this at least three times, so that the area 

 counted will be 27 spaces, each 1 mm. square. The more cells 

 counted the more accurate the results should be, but the three fields 

 should be sufficient. 



To estimate the number of cells per cubic millimetre in the blood 

 specimen used, add together the number of cells and divide by the 

 number of millimetre spaces counted. Each space is T ^ mm. X 1 mm. 

 X 1 mm. or -^ c.mm. Now multiply the average number of cells in 

 each space by 10 to find the number of cells in the diluted blood, 

 and then by 10 or 20 according as the blood was diluted, and that 

 will give the number of white cells per cubic millimetre in the blood 

 specimen, as follows: 



33 45 56 47 39 57 51 43 49 



48 57 39 55 45 61 37 61 53 



61 53 59 43 51 41 57 39 40 



142 155 154 145 135 159 145 143 142 = 1320 



X10X20 = 9777| white cells per cubic millimetre 

 of the blood examined. 



Questions. 1. What is the number of white cells per cubic 

 millimetre in the blood in the normal individual? 



2. What is the normal variation? 



3. What are some of the causes of the variations? 



C. To Count both Red and White Cells at the Same Time. 



In general the whole technique is followed out and the same 

 instruments used as when counting the red cells alone. The method 

 consists of using a diluting solution containing a stain that will stain the 

 white cells only, and then counting the red and white cells separately. 



