THE BLOOD. 161 



But of the several varieties of haemoglobinometer that which appears to 

 be the best adapted to its purpose is that invented by Professor Fleischl, 

 of Vienna. In this instrument, the amount of haemoglobin in a solution 

 of blood is estimated by comparing a stratum of diluted blood with a 

 standard solid substance of uniform tint similar spectroscopically to di- 

 luted blood. In order that the strength of color in the standard sub- 

 stance may be varied, the red tinted glass is made wedge-shaped. This, 

 which is called the comparison wedge, is cemented on to a colorless 

 plain strip of glass, and is mounted in a frame (fig. 138, P) made to 

 slide in a V-shaped groove, on the under surface of the stage of the in- 

 strument. The comparison wedge, K, is so placed that one of its longi- 



Fig 138. Fleischl's Hsemoglobinometer. 



tudinal edges bisects the circular stage-opening, so that one-half of the 

 latter is cut off by the red-tinted wedge. Into the stage-opening fits 

 a small circular trough, G, having a glass bottom, and divided into equal 

 compartments by a thin lamina. One compartment, a, is filled in the 

 manner to be presently indicated with diluted blood, and the other, #', 

 with water; the trough is so placed that the lamina is in one plane with 

 the edge of the wedge, the water compartment being above the wedge 

 and the blood compartment above the free half of the stage opening. 

 By turning the screw head, T, the frame, P, with the wedge, K, may 

 be moved backward and forward until a position is found where the in- 

 tensity of the tints due to the stratum of blood on the one hand and the 

 thickness of the wedge on the other appears to be equal. The required 

 degree of dilution is obtained by the use of small capillary tubes of a 

 capacity varying from 6 to 8 cmm. The capillary pipette is filled with 

 blood and is held over the blood compartment and its contents thor- 

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