214 



PHYSIOLOGICAL CHEMISTRY. 



FIG. 71. 



lobe of the ear of the subject by the use of soap and water, alcohol 

 and ether applied in the sequence just given. Puncture the skin 

 by means of a needle or scalpel and allow the blood drop to form 

 without pressure. Place the tip of the pipette in contact with the 

 blood drop, being careful to avoid touching the skin, and draw 

 blood into the pipette up to the point marked 0.5 or i according 

 to the desired dilution. Rapidly wipe the tip of 

 the pipette and immediately fill it to the point 

 marked 101 with Toison's or Sherrington's solu- 

 tion. Now thoroughly mix the blood and dilut- 

 ing fluid within the mixing chamber by tapping 

 the pipette gently against the finger, or by shaking 

 it while held securely with the thumb at one end 

 and the middle finger at the other. After the two 

 fluids have been thoroughly mixed the diluting 

 fluid contained in the capillary-tube below the 

 bulb should be discarded in order to insure the 

 collection of a drop of the thoroughly mixed blood 

 and diluting solution for examination. Transfer 

 a drop from the pipette to the ruled floor of the 

 counting chamber and, after placing the cover- 

 glass firmly in position, 1 allow an interval of a 

 few minutes to elapse for the corpuscles to settle 

 before making the count. Now place the slide 

 under the microscope and count the number of 

 erythrocytes in a number of squares, counting the 

 corpuscles which are in contact with the upper 

 and the right-hand boundaries of the square as 

 belonging to that square. Take the squares in 

 some definite sequence in order that the recount- 

 ing of the same corpuscles may be avoided. Of 

 course, all things being equal, the greater the 

 number of squares examined the more accurate 

 the count. It is considered essential under all 

 circumstances, where an accurate count is desired, 

 that the counting chamber shall be filled, at least twice, and the indi- 

 vidual counts made in each instance, as indicated above, before the 

 data are deemed satisfactory. 



1 If the cover glass is in accurate apposition to the counting cell Newton's 

 rings may be plainly observed. 



THOMA-ZEISS CAP- 

 ILLARY PIPETTES. 



A, Erythrocytom- 



eter; B, Leuco- 



cytometer. 



