246 PHYSIOLOGICAL CHEMISTRY. 



A wedge made for candle light cannot be used with sunlight. In addition 

 to this difficulty the wedges themselves are often at fault. They sometimes 

 fail to produce a blood red with any kind of light. 



Miescher has suggested several improvements in the Fleischl instrument 

 which render it much more accurate. Readings may be made from several 

 different dilutions from which a mean value may be taken. 



The Hemoglobinometer of Gowers. This instrument has been made in 

 several forms. The construction is essentially this. Two narrow glass 

 tubes of the same diameter are used; one receives as a standard a i per 

 cent solution of normal blood, while the other is graduated from below 

 from o to 100 degrees and is intended to receive the blood under examina- 

 tion. A measured portion of this blood, usually 20 cubic millimeters, is 

 poured into the tube and diluted with distilled water, a little at a time. 

 After each addition of water the tube is shaken thoroughly to mix and a 

 comparison made with the standard tube. When the colors are finally the 

 same, as read horizontally, that is across, not down through the tubes, the 

 degree of dilution reached in the graduated tube is noted. This indicates 

 the percentage of color present as compared with the standard. A blood 

 which can be diluted to 100 degrees (100 times the original small volume 

 taken) contains 100 per cent of the normal hemoglobin content or is nor- 

 mal, while if it can be diluted to 75 degrees only, the comparison shows 

 that this blood contains but 75 per cent of the average hemoglobin. 



In place of using blood as a standard a gelatin solution stained with picro- 

 carmine or other stain is frequently employed. But in time such color 

 standards always fade, and an abnormally high result is recorded as a 

 consequence. 



Dare's Hemoglobinometer. In this instrument the principle employed in 

 the Fleischl apparatus is used, but the comparison is made between the 

 colored glass standard and undiluted blood. The possible error due to 

 dilution is thus avoided. Some idea of the apparatus is given by the 

 illustrations above. A drop of perfectly fresh blood is placed over the 

 opening in a capillary flat cell into which it is immediately drawn, much 

 as a drop of water is drawn in between a slide and cover glass not in 

 absolute close contact, when the water is put on the edge of the cover. 

 The capillary observation cell is mounted at the end of an eyepiece through 

 which it may be clearly seen. A small portion of the colored glass standard 

 may be seen at the same time. The blood cell and red glass are evenly 

 illuminated by a candle flame placed in fixed position in front of the appa- 

 ratus. The colored glass standard is given the form of a circular disk, 

 which may be rotated by a screw motion. This disk is beveled from one 

 side to the other, giving a wedge effect as in the Fleischl apparatus. The 

 rotation of the disk brings therefore thicker or thinner portions of the edge 

 in the field of the eyepiece along with the cell holding the blood. When 

 the colors are matched the corresponding hemoglobin value is read off on 

 a scale. In practice this instrument is somewhat more convenient than the 

 Fleischl. The accuracy is about the same. 



