OXYH^MOGLOBIN. Ill 



the top of the division between the compartments. If the tip of 

 the pipette is placed slightly below the surface and the water flows 

 slowly it will not mix with the solution of blood below. This is 

 advisable in order to prevent the possibility of any of the haemo- 

 globin's passing over into the other compartment. If both com- 

 partments are filled to the top of the separating partition, so that 

 there is no meniscus at the top of the liquid, they appear, when 

 looked at from above, to be separated only by a narrow black line. 

 A little grease on the top of the partition will help to prevent a 

 mixing of the two liquids. (Some authors recommend that the 

 water be allowed to rise above the partition and a cover glass be 

 then laid on top to prevent currents.) 



Place the instrument with the large screw at the right, turn 

 the reflector so as to illuminate the solution, shade the eye from 

 other light, and move the ruby prism so that the shades of red in 

 the two compartments are the same. The figure in the scale, 

 opposite the middle of the cylinder, gives the percentage of haemo- 

 globin as compared with the average amount found in normal 

 human blood. 



With Dare's hsemoglobinometer but a single drop of blood 

 is necessary. This is drawn by pricking the skin with a needle 

 and allowed to run between two parallel plates of glass fixed at 

 a short distance apart. Comparsion is made with the color on 

 the margin of a disk which can be rotated by means of a milled 

 screw until the same shade is attained. Yellow light is trans- 

 mitted through the blood and colored glass from a candle held 

 opposite; the percentage of normal haemoglobin is read from a 

 scale on the edge of the revolving disk. The operation is simpler 

 and more expeditious than that of Fleischl. 



OXYH^EMOGLOBIN-. 



The crystalline form of oxyhsemoglobin differs when 

 its source is from different species of animal: from human 

 blood being in long prisms; from the squirrel, flat, six- 

 sided plates; and from the guinea-pig, tetrahedra. It 

 can be easily crystallized from the blood of the dog, guinea- 



