118 PHYSIOLOGICAL CHEMISTRY 



up about 9'5% of the hemoglobin, hemochromogen about 4%. 

 The corpuscles contain about 30% of hemoglobin, an amount 

 much greater than could be dissolved in an equal amount of 

 fluid, so it must be assumed that hemoglobin is held in some 

 loose combination with the other constituents of the corpuscles. 

 Hemoglobin and many of its derivatives contain iron to the 

 extent of about 3%. This iron seems to be directly connected 

 with the ability of hemoglobin to combine with oxygen. 



Oxyhemoglobin may be crystallized with comparative ease. 

 Oxyhemoglobins from different animals form crystals of greatly 

 varying form, and may be crystallized with varying degrees of 

 ease. Those easiest to crystallize are oxyhemoglobin of the 

 guinea pig, which forms tetrahedra, of the rat (rhomboids), of 

 the squirrel (hexagons), of the horse, dog, etc. Oxyhemoglobin 

 from man (long rods, rhomboids), ox, and other animals may be 

 obtained in crystalline form, but with greater difficulty. Crys- 

 tals of the types which crystallize easily may be obtained by a 

 variety of methods. That of Reichert consists in adding 1-5% of 

 solid ammonium oxalate to blood, either before or after laking 

 or defibrinating. A drop of this blood placed on a slide will 

 crystallize quickly. On standing in the ice chest very beautiful 

 large crystals form. 



Reichert and Brown have studied the oxyhemoglobin crystals 

 from the blood of a great many animals and maintain that bio- 

 logical relationships may be traced in the crystal form, since 

 oxyhemoglobins from animals of the same species crystallize in 

 similar forms. Hemoglobin is more soluble than oxyhemoglobin, 

 and is thus much more difficult to crystallize. 



Detection of Hemoglobin. In medical practice, and also in 

 medico-legal cases it often is of the greatest importance to de- 

 tect and identify hemoglobin or its derivatives. This is done in 

 a variety of ways as follows. 



Catalytic Activity of Blood. If hydrogen peroxide is added 

 to blood, or even to blood diluted to the point where the solution 

 is no longer colored, the peroxide is decomposed, and bubbles of 

 oxygen gas are given off. If the blood is first boiled, no action 



