212 PHYSIOLOGICAL CHEMISTRY. 



observed through a small telescope attached to the apparatus. It is 

 viewed through a circular opening and near this circle is a second 

 one through which a portion of a semicircular colored glass wedge, 

 is visible. These two circles are illuminated simultaneously by 

 means of the flame of a candle. The colored glass may be rotated 

 by means of a milled wheel and the point of agreement of the color 



FIG. 69. 



METHOD OF FILLING THE CAPILLARY OBSERVATION CELL OF DARE'S 



H^MOGLOBINOMETER. (Da Costd.) 



of the adjoining discs may be determined in the same way as in 

 Fleischl's hsemometer. The scale reading gives the percentage of 

 the normal quantity of haemoglobin which the blood sample under 

 examination contains. Compute the actual haemoglobin content in 

 the same manner as from the scale reading of the Fleischl haemom- 

 eter (see page 209). 



4. Tallquist's Haemoglobin Scale. This consists essentially of 

 a series of ten colors corresponding to stains produced by blood 

 containing varying percentages of haemoglobin. In using this scale 

 a drop of blood is allowed to fall on a small section of filter paper 

 and the resulting color is compared with the ten colors of the scale. 

 When the color in the scale is found which corresponds to the color 

 of the blood stain the accompanying haemoglobin value is read off 

 directly. This is a very convenient method for determining haemo- 

 globin at the bedside. There is a possibility of the colors being 

 inaccurately printed, however, and even if originally correct in tint, 

 under the continued influence of air and light they must eventually 

 alter somewhat. 



5. Thoma-Zeiss Haemocytometer. This is an instrument 

 used in "blood counting/' i. e., in determining the number of 

 erythrocytes and leucocytes. The instrument consists of a micro- 

 scopic slide constructed of heavy glass and provided with a central 

 counting cell (see Fig. 70, p. 213). This cell, with the cover-glass 



