BLOOD ANALYSIS 



309 



The diluting is done in a small round-bottomed flask as shown in Fig. 99. 

 Several of these flasks should be kept on hand in a wooden rack which will hold 

 them in an upright position. Each flask is provided with a paraffined, or smooth 

 cork stopper. 



In the older counting chambers the floor of the chamber is circular and the 

 counting is done in the center of this space. The corpuscles are therefore counted 

 in the center of a capillary, circular film where on account of surface tension their 

 number is slightly greater than elsewhere. This source of error is avoided in the 

 new counting chamber (Fig. 102) in which the floor is represented by the upper 

 surface of a piece of glass 25 mm. long and 5 mm. wide which is rounded off at both 

 ends and divided into two portions by a groove 1.5 mm. wide through the center. 



FIG. 99. BURKER'S PIPETTES, MIXING FLASKS AND COUNTING CHAMBER. 



At each side of this floor piece, separated from it by a groove is a glass plate 

 (7.5 mm. X 21 mm.) of such height that the space between the floor of the cell 

 and a cover-glass placed across the plates is o.ioo mm. A cover-glass 23 mm. 

 long and 21 mm. wide with rounded polished edges is used so that the rounded 

 ends of the floor piece project beyond it. The chamber is provided with clamps 

 to press the cover-glass firmly upon both plates (Fig. 99). 



The ruling on each portion of the floor piece is that shown in Fig. 100, which 

 will be explained below. 



Measuring the Diluting Fluid. Four thousand nine hundred and seventy-five 

 cu. mm. of diluting fluid (Hayem's) are measured out into the diluting flask. To 

 do this the pipette is filled by suction to slightly above the mark and the rubber 

 tube is carefully clamped off. Then with a soft piece of linen the tip is wiped dry. 

 The meniscus is then accurately adjusted to the mark by lightly touching the point 

 of the pipette to the cleaned tip of the finger. The pipette is then inserted into 



