3 io 



PHYSIOLOGICAL CHEMISTRY 



the diluting flask and with the tip nearly touching the bottom of the flask the fluid 

 is allowed to run out. The time of the flow should be about forty seconds and is 

 controlled by placing the tip of the index-finger loosely upon the mouthpiece. 

 The pipette is emptied completely by alternately blowing through it and touching 

 it to the wall of the flask slightly above the level of the liquid. The drops clinging 

 to the wall are united with the bulk of the liquid by a suitable motion of the flask. 

 The flask is then stoppered, care being taken from now on that none of the liquid 

 ever touches the neck of the flask or the stopper. 



Taking the Blood Sample. Usually the best time to draw the blood is before 

 breakfast. For a single determination the author prefers to draw it from the tip 

 of the fourth finger of the left hand. For repeated determinations it is well to 

 change off between third, fourth and fifth fingers of left hand. The temperature 

 of the room should not be below i7C. to prevent an undue contraction of the 

 cutaneous vessels. The instrument used to puncture the finger should have a 

 chisel-shaped point which is preferable to the ordinary lancet-shaped point. The 



53 C 

 01 



FIG. zoo. RULING OF BURKER COUNTING CHAMBER. 



first drop of blood is wiped off. Into the second one the tip of the pipette is in- 

 serted and blood is drawn in until the meniscus is even with or a little beyond the 

 mark. The tip is then wiped off without touching the capillary opening and the 

 observer assures himself that the column of blood extends to the very end of the 

 capillary. The meniscus is then accurately adjusted to the mark. 



Mixing of the Blood and Diluting Fluids. The tip of the pipette is now dipped 

 into the diluting fluid which has been measured into the flask and the blood is 

 slowly blown out. The blood having a much higher specific gravity than the 

 Hayem's fluid sinks to the bottom. The pipette is then filled with the pure super- 

 natant diluting fluid and emptied again, care being taken to avoid air 'bubbles. 

 This is repeated until the blood is removed as completely as possible. To mix the 

 blood and diluting fluid the flask is rotated for two minutes in spiral curves of 

 continually decreasing radius. The motion should be alternately clockwise and 

 counterclockwise. After complete mixing the pipette is rinsed out several times 

 with the diluted blood. 



