LABORATORY MANUAL OF PHYSIOLOGY. 



chamber, this should be constantly rotated between the fingers so 

 as to facilitate the mixture and avoid error through coagulation. 



The other part of the instrument is the micrometer slide upon 

 which the diluted blood is evenly spread for counting the corpus- 

 cles. This consists of a glass slide (Fig. 22), upon which is mounted 

 a covered disc, m, a square millimetre of which is subdivided by a 

 dividing engine into 400 squares of one-twentieth millimetre each. 

 The micrometer, m, is surrounded by an annular cell, c, the sides 

 of which project one-tenth millimetre above the surface of m. This 

 cell is closed by a thin flat glass cover, so that the cubic space in- 

 cluded between each small square of the micrometer and the cover 

 would be ^nnr f a cubic millimetre. 



To find the number of corpuscles in a cubic millimetre of undi- 

 luted blood, multiply 4000 by the dilution and this by the total 

 number of corpuscles counted. This result is then divided by the 

 number of small squares counted. If the blood has been drawn 

 only to the 0.5 mark in the diluting pipette, the blood dilution is 

 i to 200 and this number must be substituted for the factor 100 in 

 the formula given above. With normal blood, the higher dilution 

 is advisable. 



Procedure. Thoroughly cleanse the tip of the finger or, prefer- 

 ably, the lobe of the ear, with soap and water. Wipe off with a 

 cloth wet with alcohol. Dry thoroughly. With a sterilized needle, 

 or a sharp pen with one nib broken off, make a quick stab of the 

 ear or the finger. Wipe off the first drop of blood. Blood should 

 ooze freely from the puncture without pressure. Insert the point 

 of the pipette well into the blood drop and carefully draw in blood 

 to the 0.5 mark on the stem of the pipette. With a cotton cloth 

 wipe off all blood adhering to the outside of the pipette. Dip the 

 end of the pipette into the diluting fluid and draw this in through 

 the stem and into the ball until the 101 mark is reached. The pi- 

 pette should be gently rotated while the filling is going on, in order 

 that the mixture of the blood and diluting fluid may be assured 

 through the movements of the glass bead in the ball. Close both 

 ends of the pipette with thumb and forefinger and shake well. 



[60] 



