/'// YSIOLOGIL ',//, ILK MA TOLOG Y. 263 



pipette, blow out a drop, place the diluted blood on the 

 counter and count as before. If the two countings are 

 nearly the same, this will be sufficient; if there is much 

 difference, a third field should be counted and an aver- 

 age taken of the two fields nearest alike. Divide the 

 number of corpuscles by the number of squares; multiply 

 this by 200 to make up for the dilution and then by 400, 

 because each square is equivalent to one four-hundredth 

 of a cubic millimeter. This will give the number of cor- 

 puscles per cubic millimeter. Count the corpuscles on 



FIG. 38b. 



FIG. 38b. Showing the right and the wrong way to fill a Zeiss count- 

 ing cell. a. Too little blood, b. Too much blood, c. The proper 

 amount of blood. 



one half the boundary of each square but do not count 

 them on the other half. 



4. Precautions. See that the blood corpuscles are evenly 

 scattered over the field. (Fig. 39). If they are clus 

 tered, it shows faulty technique and the counting dilution 

 must be prepared again with more care. Clean counter 

 and pipette first with water and then with alcohol after 

 using, being careful to leave the tube perfectly dry. The 

 pipette is easily broken. Thefine lineson the counter are 

 injured by rubbing with a coarse cloth. The cover glass 



