OPTICAL PROPERTIES OF BLOOD. 



245 



until the liquids in the two compartments of the cell appear to have the 

 same color. The color in a certain portion of the wedge is intended to 

 correspond to normal blood, or blood with 100 per cent of the normal 

 oxyhemoglobin, and degrees placed at proper intervals along the wedge 

 represent corresponding higher or lower percentages. For example, if 

 when the colors in the two compartments are matched the reading on the 

 \vedge scale is 97, it means that the blood contains color due to 97 per cent 

 of the normal or average oxyhemoglobin content. 



FIG. 21. Dare's hemoglobinometer. R, 

 milled wheel acting by a friction bearing on 

 the rim of the color disc ; S, case inclosing 

 color disc, and provided with a stage to which 

 the blood chamber is fitted ; T, movable wing 

 which is swung outward during the observa- 

 tion, to serve as a screen for the observer's 

 eyes, and which acts as a cover to inclose the 

 color disc when the instrument is not in use ; 

 U , telescoping camera tube, in position for 

 examination ; V ' , aperture admitting light for 

 illumination of the color disc ; X, capillary 

 blood chamber adjusted to stage of instru- 

 ment, the slip of opaque glass, W , being 

 nearest to the source of light ; Y, detachable 

 candle-holder; Z, rectangular slot through 

 which the hemoglobin scale indicated on the 

 rim of the color disc is read. 



This Fleischl instrument is one of the best in principle but it must be 

 carefully used to furnish good results. The color of the. wedge does not 

 correspond to blood color unless a certain kind of white light is employed. 



FIG. 22. Horizontal Sec- 

 tion of Dare's Hemoglobin- 

 ometer, in which the arrange- 

 ment of parts is clearly 

 shown. L is the standard 

 wedge-shaped color disc. 

 The blood is inclosed between 

 the glass plates O and P and 

 is illuminated by the flame 7. 

 The eye observes the blood 

 and the color scale through 

 the apertures M and M'. 



