304 PHYSIOLOGICAL CHEMISTRY 



4. Tallquisf s Hemoglobin Scale. This consists essentially of a 

 series of ten colors corresponding to stains produced by blood contain- 

 ing varying percentages of hemoglobin. 



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 hemoglobin value is read off directly. 



This is a very convenient method for determining hemoglobin 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 Hemocytometer. This is an instrument used in 

 "blood counting, " i.e., in determining the number of erythrocytes and 

 leucocytes. The instrument consists of a microscopic slide constructed 

 of heavy glass and provided with a central counting cell (see Fig. 95, 



FIG. 95. THOMA-ZEISS COUNTING CHAMBER. (Da Costa.) 



below). This cell, with the cover glass in position, is exactly o.i mm. 

 deep. The floor of the cell is divided by delicate lines into squares each 

 of which is 1/400 sq. mm. in area (see Fig. 97, page 306). The volume 

 of blood, therefore, between any particular square and the cover glass 

 above must be 1/4000 cu. mm. Accompanying each instrument are 

 two capillary pipettes (Fig. 96), each constructed with a mixing bulb 

 in its upper portion. Each bulb is further provided with an enclosed 

 glass bead which is of great assistance in mixing the contents of the 

 chamber. The stem of each pipette is graduated in tenths from the 

 tip to the bulb. The final graduation at the upper end of the bulb is 

 101 on the pipette used in mixing the blood sample in which the ery- 

 throcytes are counted (erythrocytometer, see Fig. 96), and n on 

 the pipette used in mixing the blood sample for the leucocyte count 

 (leucocytometer, see Fig. 96). In making "blood counts" with the 

 hemocytometer it is necessary to use some diluting fluid. Two very 

 satisfactory forms of fluid for this purpose are Toison's and Sher- 



