308 PHYSIOLOGICAL CHEMISTRY 



of the diaphragm-fields in duplicate specimens and the calculation made 

 in the same manner as explained above. 



If the leucocytes are counted in a separate specimen of blood ordina- 

 rily the diluting fluid is 0.3-0.5 per cent acetic acid, a fluid in which the 

 leucocytes alone remain visible. Under these conditions the dilution is 

 customarily made in the pipette having 1 1 as the final graduation. The 

 capillary portion is of larger caliber and so requires a greater amount of 

 blood to fill it to the 0.5 or i mark than is required in the use of the other 

 form of pipette. In counting the leucocytes according to this method it 

 is customary to draw blood into the pipette up to the i mark and im- 

 mediately fill the remaining portion of the apparatus to the 1 1 gradua- 

 tion with the 0.3-0.5 per cent acetic acid. It then remains to count the 

 number of leucocytes in the whole central ruled portion of 400 squares. 

 This should be done in duplicate samples and the calculation made as 

 follows :. 



Number of leucocytes in 800 v _ Number of leucocytes per cubic 



squares millimeter. 



6. Barker's Hemocytometer. ! This is an improved apparatus 2 for the more 

 accurate counting of erythrocytes than is possible by the Thoma-Zeiss apparatus. 

 The principles involved are somewhat different from those in force with the latter 

 apparatus. For example, the blood is diluted in a separate vessel, not in the pipette 

 with which the sample is drawn, and furthermore the cover-glass is applied to the 

 counting chamber and clamped in place before the diluted blood is applied to the 

 ruled area. Hayem's solution 3 is used as the diluting fluid. Toison's solution is 

 not satisfactory for use with the Biirker counting chamber as its viscosity is too 

 great. The corpuscles settle rapidly in Hayem's fluid as the specific gravity of the 

 fluid is 1015 whereas that of the erythrocytes is 1090. 



The pipette for measuring the quantity of blood (Fig. 99, upper pipette) has a 

 point which is not ground dull but is polished. This allows of better judgment in 

 deciding whether the column of blood extends to the very tip. The volume of 

 the pipette between tip and mark is 25 cu. mm. The mark extends all the way 

 around the tube so that errors of parallax may be avoided. 



The pipette for measuring the diluting fluid (Fig. 99, middle pipette) also has 

 a polished point and circular mark and delivers 4975 cu. mm. This volume of 

 diluting fluid with 25. cu. mm. of blood gives a dilution of i : 200. Both pipettes 

 are provided with a piece of rubber tubing and mouthpiece. 



For transferring the diluted blood from the diluting flask to the chamber a 

 plain pipette provided with a rubber cap is used (Fig. 99, lower pipette). It is 

 filled by pressing the cap slowly with the index-finger, inserting the tip into the 

 liquid and then releasing the pressure. 



1 Biirker: P finger's Archiv., 142, 337, 1911; Munch, med. Woch., 59, pp. 14 and 89, 1912. 



2 Manufactured by C. Zeiss, Jena. 



3 Hayem's solution has the following formula: 



Mercuric chloride o. 25 gram. 



Sodium chloride o . 5 gram. 



Sodium sulphate 2 . 5 grams. 



Distilled water 100 . o grams. 



