2O2 



MICROMETRY AND BLOOD PREPARATIONS 



is probably not over 10% after a little experience. 

 is not kept in the dark, the tints tend to fade. 



If the colored plate 



To COUNT BLOOD-CORPUSCLES 



The instrument almost universally used is the Thoma-Zeiss haemacy- 

 tometer. The apparatus consists of two pipettes, one for leukocytes, 

 graduated to give a dilution of i to 10 or greater; the other for red cells 

 to give a dilution of a i to 100 or greater. The white pipette has the 

 mark n above the bulb and the red pipette the mark 101. In addition, 

 there is a counting chamber. 



This consists of a square of glass with a round hole in the center. Occupying the 

 center of this round hole is a circular disc of glass of less diameter, so that an encirc- 



ling channel is left. The square and the circle 

 of glass are cemented to a heavy glass slide. 

 The surfaces of each are absolutely level and 

 highly polished. That of the circular disc is 

 ruled into squares of varying size and is exactly 

 Ho rnm. below the level of the surface of the sur- 

 rounding glass square. 



When a polished piano-parallel cover- 

 glass rests on the shelf, as the outer square 

 glass is termed, there is a space left be- 

 tween its under-surface and the ruled disc 

 of o.i mm. The channel around the disc 

 is termed the moat or ditch. 



The most desirable rulings are those of Tiirck 

 and of Zappert. In these the entire ruled surface 

 consists of nine large squares, each i mm. square. 

 These are subdivided, and in the central large 

 small squares used for averaging the red cells. 



FIG. 5 3 . Thomas-Zeiss 

 blood counter showing pipette, 

 counting chamber, and ruled 

 field. (Greene.} 



the 



square are to be found 

 These small squares are Ho rnm. square and are arranged in nine groups of 16 

 small squares by bordering triple-ruled lines. As the unit in blood counting is 

 the cubic millimeter, if one counted all the white cells lying within one of the 

 large squares (i mm. square), he would have only counted the cells in a layer 

 one-tenth of the required depth, so that it would be necessary to multiply the 

 number obtained by 10. This product, multiplied by the dilution of the blood, 

 would give the number of white cells in a cubic millimeter of undiluted blood. 

 Some workers prefer the Biirker hamacytometer. In this there are two ruled 

 wedge-shaped pieces of glass, separated at their bases, which take the place of 

 the ruled disc of the Thoma apparatus. Two oblong pieces of glass are on either 

 side of the ruled wedges and are o.i mm. higher, thus taking the place of the shelf. 

 Clamps fix a cover-glass on these shelves giving a space Ho mm. over the ruled sur- 



