232 



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 Blood=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: a, Slide used in counting ; b, sectional view ; 

 f, a portion of ruled bottom of the well ; </, 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 o. 5 gm. 



Sodium chlorid j .o gm. 



Sodium sulphate 5.0 gm. 



Distilled water 200.0 c.c. 



Toisori 1 s Fluid (as given by V. Kahlderi) : 



Methyl violet 58 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. ) l.o gm. 



Sodium sulphate (C. P.) 8.0 gm. 



Distilled water 80.0 c.c. 



