COUNTING THE RED CORPUSCLES 5 



The Zappert-Ewing ruling, the one to use preferably, has besides 

 this central 400 squares additional lines as shown in Fig. 4 giving 

 a ruled space of nine sq. mm. With each instrument are thick 

 and thin cover glasses with plane ground surfaces. The thick 

 covers give more accurate results. The mixing pipette is a cap- 

 illary tube divided into ten equal divisions and terminated by a 

 bulb of 100 times the capacity of the tube. Thus when blood is 

 drawn to the mark 1 on the tube and diluting fluid is drawn to 

 the mark 101 a dilution of 1:100 is obtained. The bulb contains 

 a glass bead to facilitate mixing the blood and diluting fluid. 

 Attached to the pipette is a flexible rubber tube having a mouth- 

 piece. The pipettes are made in a long and a short form. The 

 longer form is preferable as the shorter form is constricted at the 

 point rendering it liable to become clogged and making it very 

 difficult to clean should it become clogged. 



Method of using. The bottle of diluting fluid should be 

 within reach and should be unstoppered. In using, the point of 

 the pipette is immersed into a freshly exuded drop of blood. With 

 gentle suction blood is drawn up to one of the divisions on the tube, 

 the pipette is withdrawn and the blood on the outside of the tube 

 quickly wiped off. As quickly as possible it is placed in the dilut- 

 ing fluid with the point well below the surface and the diluting 

 fluid drawn in filling the pipette exactly to the mark 101. The 

 blood and diluting fluid are then thoroughly mixed by shaking 

 and rotating the pipette. Care must be taken to draw in fresh 

 blood, the slightest clotting will necessitate cleaning the pipette 

 and repeating the operation. Care must also be taken not to 

 draw in air with the blood or with the diluting fluid. If any air 

 should be drawn in it is well to at once draw in diluting fluid to 

 prevent the blood clotting in the pipette as it is difficult to remove 

 clotted blood. With the blood thoroughly mixed with the diluting 

 fluid it is not necessary to make the count at once. If the pipette 

 is kept in a horizontal position it may be carried some distance. 

 It is better to make the count as soon as possible, though the 

 blood will keep for several hours unchanged in the diluting fluid. 



Filling the counting chamber. When ready to fill the count- 

 ing chamber, the pipette should be shaken and rotated to get an 

 even distribution of the corpuscles. One minute will usually be 

 found sufficient for this. The diluting fluid in the long arm of the 



