3 02 



PHYSIOLOGICAL CHEMISTRY 



are placed directly above and below the graduation. Each cross-line 

 corresponds to i/ioo of the volume of the capillary tube from the tip 

 to the i graduation. 



A o.i per cent solution of sodium carbonate is used to dissolve the 

 stroma of the erythrocytes and so render the blood solution perfectly 

 clear. If this is not done the color of the blood solution invariably ap- 

 pears darker in tone than that of 

 the colored glass wedge. A freshly 

 prepared sodium carbonate solu- 

 tion should be used in order that 

 the clearness of the solution may 

 not be marred by the presence of 

 sodium bicarbonate. 



3. Dare's Hemoglobinometer 

 (Fig. 92). This instrument, as 

 the name signifies, is used for the 

 determination of hemoglobin. In 

 using either FleischPs hemometer 

 or the instrument as modified by 

 Miescher the blood is diluted for 

 examination, whereas with the 

 Dare instrument no dilution is re- 

 quired. This probably allows of 

 rather more accurate determina- 

 tions than are possible with the 

 old Fleischl apparatus. 



The instrument consists essen- 

 tially of the following parts: (i) 

 A capillary observation cell, (2) a 

 semicircular colored glass wedge, 

 (3) a milled wheel for manipulat- 

 ing 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 illumi- 

 nated by the candle flame, (6) a scale graduated in percentages of the 

 normal amount of hemoglobin, (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 observation is being made. 



FIG. 92. DARE'S HEMOGLOBINOMETER. 

 (Da Costa.} 



R, Milled wheel acting by a friction bear- 

 ing on the rim of the color disc; S, case in- 

 closing color disc, and provided with a stage 

 to which the blood chamber is fitted; T, 

 movable wing which is swung outward dur- 

 ing the observation, to serve as a screen for 

 the observer's eyes, and which acts as a 

 cover to inclose the color disc when the in- 

 strument is not in use; U, telescoping cam- 

 era tube, in position for examination; V, 

 aperture admitting light for illumination of 

 the color disc; X, capillary blood chamber 

 adjusted to stage of instrument, the slip of 

 opaque glass, W, being nearest to the source 

 of light; Y, detachable candle-holder; Z, 

 rectangular slot through which the hemo- 

 globin scale indicated on the rim of the 

 color disc is read. 



