266 LABORATORY GUIDE IN PHYSIOLOGY. 



Operation. Obtain blood as described in exercise LVI 

 and dilute with the above solution. Bring upper line of 

 ruled square to bottom of the square of the field; then the 

 field of the microscope will correspond to field one in the 

 figure. Count all the white cells in the field. Then fix 

 the eye on a cell in the upper margin and bring it to the 

 lower edge of the field; count this field and proceed in the 

 same way to field 3. Turn stage back to ruled space, us r 

 ing the border to indicate where to begin to count. Count 

 fields 4, 5 and 6; turn back to ruled square and proceed 



FIG. 42. 

 FIG. 42. Position of solution tipped to receive pipette horizontally. 



to 7, 8, 9; turn back to ruled square and count 10, U and 

 12. For a larger count, proceed in the same manner 

 from the central ruled space to count the additional 

 squares enclosed with dotted lines. The acetic acid in 

 the diluting solution renders the red corpuscles transpar- 

 ent or dissolves them entirely. If this does not so ap- 

 pear, the acid is too weak and more should be used to 

 obtain the desired results. 



4. Precautions. Make a good deep puncture. Have a large 

 drop of blood. Remember that the bore of this pipette 

 is larger than that of the pipette for red corpuscles and 

 the solution will run out if the pipette is held perpendic- 

 ularly. (Fig. 42.) The suction also must be more gentle 



