72 



GENERAL CHEMICAL AND PHYSICAL CHARACTERS 



individuals of a given species is not of uniform composition, that this pos- 

 sible source of difference need scarcely be considered. That important errors 

 in analysis have occurred seems evident, as, for instance, in the very low 

 C, Fe, and S percentages found by Zinoffsky in his analyses of the hemo- 

 globin of the horse, and in the differences in the percentages and ratios of 

 Fe and S shown by the record of different analyses of the hemoglobin from 

 individuals of the same species (table 26). Another source of error is to be 

 found in the different methods for determining the N content, but doubt- 

 less the most important source is in abnormalities of the substance itself 

 which have been due to the methods of preparation. The attempts to ob- 

 tain pure hemoglobin by repeated crystallization have, instead of yielding 

 a pure product, given rise to artifacts, each recrystallization adding another 

 step in the denaturalization and disintegration of the molecule. 



TABLE 26. The ratios of Fe to S according to the analyses of various observers. 



The great instability of the hemoglobin molecule has been shown in 

 various ways, and the tenacity with which this and other proteins mechan- 

 ically or chemically cling to or combine with certain substances has like- 

 wise been proved. Hoppe-Seyler (Archiv f. path. Anat. u. PhysioL, 1864, 

 xxix, 223) in his earliest researches on hemoglobin found that neither 

 concentrated solutions nor crystals of hemoglobin remain unchanged for 

 even 24 hours at ordinary temperature; that hemoglobin undergoes partial 

 decomposition when dried by the aid of an air-pump and sulphuric acid; 

 and that with each recrystallization there is formed an insoluble residue 

 in the form of a derivative; Halliburton (Chemical Physiology and Pathol- 

 ogy, 1891, 287) states that, even when hemoglobin is dried in a Torricellian 

 vacuum at 40, not only is hematin and an insoluble protein formed but 

 some of the water of crystallization is driven off. He also found that 

 repeated crystallization of the hemoglobin of the squirrel ultimately changes 

 the form of the crystals from hexagonal plates to rhombic prisms, or a 

 mixture of these with rhombic tetrahedra. Moreover, the crystals of 

 hemoglobin that have been analyzed have been prepared by the "alcohol 

 method," and presumably purified by repeated recrystallization, a method 

 which of itself makes it practically absolutely impossible to obtain a normal 

 hemoglobin. Alcohol denaturalizes hemoglobin, as it does other proteins. 



