SLOOD. 



This is to obtain a uniform distribution of the corpuscles through- 

 out the mixture. 



To Fill the Counting Cell. Blow out three or four drops of the 

 diluted blood from the pipette. Now allow a small drop to flow 

 upon the disc of the counting chamber. Cover quickly, pressing 

 the cover gently down until Newton's rings are seen. These are 

 the spectrum colors due to refraction between the two layers of 

 glass. They do not appear if there is any fluid or dirt between the 

 cover and the cell. If any fluid runs over into the moat between 

 the cell and the micrometer, the slide will have to be cleaned and 

 another drop of the diluted blood taken. Repeat until a satis- 

 factory specimen for counting is obtained. 



Allow several minutes for the corpuscles to sink to the bottom of 

 the cell upon the ruled squares. It is obvious that the counting cell 

 must ke kept in the horizontal position. Place this upon the stage 

 of a microscope and count the corpuscles in all the squares. For 

 convenience of counting, the micrometer is divided into sixteen 

 large squares by double lines, and these, in their turn, are sub- 

 divided into the small squares already mentioned. Count several 

 specimens, in this way, and take the average. Compare the 

 blood of various students. 



To Clean the Cell and Pipette. The cell should be carefully rinsed 

 with distilled water and dried with a soft cloth or absorbent cot- 

 ton. The cover should be treated in the same way. Neither alco- 

 hol nor ether should be used since they will coagulate the albumin 

 of the blood. In cleaning the pipette first blow out any blood 

 mixture remaining. Fill with distilled water several times. If all 

 traces of blood are not removed in this way, rinse with an aqueous 

 solution of hydrogen peroxide and again wash out with distilled 

 water. Now draw alcohol through by suction and follow this with 

 ether, drawing through a stream of air until the pipette is 

 thoroughly dry. This is manifest when the glass bead enclosed in 

 the bulb of the pipette no longer adheres to the sides. 



Counting the White Corpuscles. Since there is a much smaller 

 number of leucocytes than of red corpuscles, the dilution required 



[61] 



