2 3 2 



THE CIRCULATORY SYSTEM. 



examined with a fragment of a cover-glass. The lung may also be ex- 

 amined, but here the incision must be farther forward. 



Counting BIood=cells. The instrument now generally used for this 

 purpose is the Thoma-Zeiss hemocytometer. This apparatus consists of 

 two parts : pipettes by means of which the blood is diluted 100 times, 

 when counting red, or 10 times when white blood-cells are to be counted, 

 and a glass slide, on which there is a small well of known depth, the bot- 

 tom of the well being divided off into small squares. The pipette used when 

 counting the red cells consists of a capillary tube, near the middle of 

 which there is an ampullar enlargement. This is so graduated that the 

 cubical contents of the capillary tube is just one-hundredth part of the 

 cubical contents of the ampulla. The blood to be examined is drawn 

 into the capillary tube to a line marked i (just below the ampulla); the 

 end of the pipette is then inserted into the diluting fluid, and this is 

 sucked up until the diluted blood reaches a line marked 101 (just above 



Fig. 179. Thoma-Zeiss hemocytometer: , Slide used in counting ; l>, sectional view ; 

 c y a portion of ruled bottom of the well ; d, pipette. 



the ampulla). The pipette is then carefully shaken to mix thoroughly 

 the blood and the diluting fluid. 



Either of the following two solutions may be used for diluting the 

 blood : 



Hay em' 's Solution : 



Bichlorid of mercury 0.5 gm. 



Sodium chlorid i.o gm. 



Sodium sulphate 5.0 gm. 



Distilled water 2CO.O c.c. 



Toisorf s Fluid {as given by V. Kahlderi) : 



Methyl violet 5 B 0.025 gm. 



Neutral glycerin 30.0 c.c. 



Distilled water 80.0 c.c. 



Mix the methyl violet with the glycerin and distilled water ; to this 

 solution is added 



Sodium chlorid (C. P.) i.o gm. 



Sodium sulphate (C. P.) 8.0 gm. 



Distilled water . 80.0 c.c. 



