2IO 



PHYSIOLOGICAL CHEMISTRY. 



FIG. 67. 



than in the unmodified apparatus of Fleischl. (4) Before reading 

 the percentage as indicated by the scale, the chamber is covered 

 with a glass and a diaphragm which sharply define the field on 

 all sides without the formation of a meniscus. 



The measuring pipette is constructed essentially the same as the 

 pipettes which accompany the Thoma-Zeiss apparatus (see page 214). 

 The capillary portion, however, is graduated i, ^3 and J^ which 

 enables the observer to dilute the blood sample in the proportion 

 of i : 200, i : 300 or i : 400 as he may desire. If there is diffi- 

 culty ,in drawing in the blood exactly to one of the graduations 

 just mentioned the amount of blood above or below the volume in- 

 dicated by the graduation may be determined by means of certain 



delicate cross-lines which are 

 placed directly above and 

 below the graduation. Each 

 cross-line corresponds to %oo 

 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 invari- 

 ably appears darker in tone 

 than that of the colored glass 

 wedge. A freshly prepared 

 sodium carbonate . solution 

 should be used in order that 

 the clearness of the solution 

 may not be marred by the 

 presence of sodium bicarbo- 

 nate. 



3. Dare's Haemoglobin- 

 ometer (Fig. 67). --This 

 instrument, as the name sig- 

 nifies, is used for the determination of haemoglobin. In using 

 either Fleischl's hgemometer or the instrument as modified by 

 Miescher the blood is diluted for examination whereas with the 



DARE'S ELEMOGLOBINOMETER. (Da Costa.) 



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 cham- 

 ber is fitted; T, movable wing which 

 is swung outward during 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 instrument is not in 

 use ; U, telescoping camera tube, in posi- 

 tion 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 haemoglobin scale indi- 

 cated on the rim of the color disc is read. 



