BLOOD. 



211 



Dare instrument no dilution is required. This probably allows of 

 rather more accurate determinations than are possible with the old 

 Fleischl apparatus. 



The instrument consists essentially of the following parts : ( i ) 

 A capillary observation cell, (2) a semicircular colored glass wedge, 

 (3) a milled wheel for manipulating the wedge, (4) a candle used 

 to illuminate portions of the capillary observation cell and the 

 colored wedge, (5) a small telescope used in the examination of 

 the areas illuminated by the candle flame, (6) a scale graduated in 

 percentages of the normal amount of haemoglobin, (7) a hard 

 rubber case, (8) a movable screen attached to the case. 



The capillary observation cell is formed of two small, polished 

 rectangular plates of glass, one being transparent and the other 

 opaque. When held in position on the instrument, by means of a 

 small metal bracket, the opaque portion of the cell is nearer the 

 candle and thus serves to soften the glare of light when an obser- 

 vation is being made. The transparent portion of the cell is directly 

 over a circular opening in the case, through which the blood speci- 

 men is viewed by means of the small telescope. 



The semicircular colored glass wedge is so ground that each 

 particular shade of color corresponds to that possessed by fresh 

 blood which contains some definite per- 

 centage of haemoglobin. It is mounted 

 upon a disc which may be manipulated 

 by the milled wheel in such a manner as 

 to bring successive portions of the wedge 

 in position to be viewed through a cir- 

 cular opening contiguous to the opening 

 through which the blood specimen is 

 viewed. For a further description of the 

 instrument see Figures 67, 68 and 69, on 

 pages 210, 211 and 212, respectively. 



In using the Dare hsemoglobinometer 

 proceed as follows : Puncture the finger- 

 tip or lobe of the ear of the subject by 

 means of a needle or scalpel and, after a HORIZONTAL SECTION OF DARE'S 



H^MOGLOBINOMETER. 



drop of blood of good proportions has (Da Costa.) 



formed, place the flat capillary observa- 

 tion cell in contact with the drop and allow it to fill by capillary 

 attraction (Fig. 69, page 212). Replace the cell in its proper place 

 on the instrument. When in position, a portion of this cell may be 





