430 



BLOOD AND LYMPH. 



of this element. According to recent analyses, the proportion of 

 iron in hemoglobin is .constant, lying between 0.33 and 0.34 per 

 cent.* The amount of hemoglobin in blood may be determined, 

 therefore, by making a quantitative determination of the iron. 

 The amount of oxygen with which hemoglobin will combine may 

 be expressed by saying that one molecule of oxygen will be fixed for 

 each atom of iron in the hemoglobin molecule In the decomposi- 

 tion of hemoglobin into globin and hematin, which has been spoken 

 of above, the iron is retained in the hematin. 



Crystals. Hemoglobin may be obtained readily in the form of 

 crystals (Fig. 181). As usually prepared, these crystals are really 



oxyhemoglobin, but it has 

 been shown that reduced 

 hemoglobin also crystallizes, 

 although with more diffi- 

 culty. Hemoglobin from 

 the blood of different ani- 

 mals varies to a marked de- 

 gree in respect to the power 

 of crystallization and the 

 form of the crystals, but in 



W I WT \ *^ e various species of any 



\0^ M& ^ ^r one S enus the crystals be- 



JHr ^^^^^^ ^ on ^ ^ one cr ystallographic 

 ^^^^ ^K^^ ^^ group. From the blood of 



the rat, dog, cat, guinea-pig, 

 and horse crystals are read- 

 A ^BL ily obtained, while hemo- 



^^^^fc ^^V globin from the blood of 



man and of most of the ver- 

 tebrates crystallizes much 

 less easily. Methods for 

 preparing and purifying 

 these crystals will be found 

 in works on physiological 

 chemistry. To obtain speci- 

 mens quickly for examina- 

 tion under the microscope, 

 one of the most certain 



methods is to take some blood from one of the animals whose hemo- 

 globin crystallizes easily, place it in a test-tube, add to it a few drops 

 of ether, shake the tube thoroughly until the blood becomes laky, 

 that is, until the hemoglobin is discharged into the plasma, and 

 then place the tube on ice until the crystals are deposited. Small 

 portions of the crystalline sediment may then be removed to a glass 

 * Butterfield, "Zeit. f. physiol. Chemie," 62, 173, 1909. 



Fig. 181. Crystallized hemoglobin (after 

 trey): a, 6, Crystals from venous blood of man- 

 c, from the blood of a cat; d, from the blood of 

 a guinea pig: e, from the blood of a hamster; 

 /, from the blood of a squirrel. 



