ALBUMINS OR PROTEINS. 125 



degrees. 1 The crystalline separation of oxyhemoglobin suddenly occurs 

 after standing for some time on ice. As the solubility of the oxyhemo- 

 globins varies according to their animal origin, it is necessary to use 

 varying quantities of water for dissolving them. Thus, in order to 

 obtain the oxyhemoglobin of the cat, it has been found convenient to 

 use an equal volume of water in dissolving the blood corpuscles. 2 

 Crystals may also be obtained by salting out with ammonium sulphate, 

 and dialysis with alcohol. Hemoglobin 3 and methemoglobin 4 can also 

 be obtained in crystalline form. 



Oxyhemoglobin can be redissolved in water at 37-40 degrees, and 

 recrystallized by the addition of alcohol in the manner previously described. 

 When obtained from different animals it crystallizes in various forms: 

 thus the crystals obtained from the squirrel are hexagonal; those from the 

 horse are orthorhombic. 



Crystals from insect blood have also been described. H. Landois 5 

 has obtained crystals from the blood of caterpillars, Pupidce, beetles, and 

 wasps, simply by evaporation. It is questionable whether these were albu- 

 min crystals. Crystals have also been isolated from the red sea-algae, 

 Rhodophycece, or Floridece. The Cyanophycece give a crystalline coloring 

 matter called phycocyan. More exact knowledge regarding the compo- 

 nents of these albumins is not yet at hand. 6 



Not only are all the external appearances of these crystals identical with 

 those of real crystals, but crystallographical investigations have shown 

 no differences. With the exception of those albuminous " plant crystals " 

 which belong, in part, to the regular system, they are all doubly refractive 

 towards polarized light. As a whole, however, only a few exact optical 

 investigations of albumin crystals have been made. 



We have intentionally devoted considerable space to the discussion of 

 these individual crystals. It is a matter of the greatest importance to us 

 in our investigations into the chemistry of albumins. Are we justified, 

 or not, in characterizing a protein substance, as pure? Let us see what 

 conclusions we can draw from the crystalliz ability of the proteins. The 

 attempt has been made to decide whether a protein was homogeneous by 

 means of an elmentary analysis. We have already shown that it is out 

 of the question to decide the question in this way. It is a well-known 



1 Cf. F. Hoppe-Seyler: Med.-chem. Untersuch. Vol. 2, p. 181, 1867. O. Zinoffsky: Z. 

 physiol. Chem. 10, 16 (1885). 



2 E. Abderhalden: Z. physiol. Chem. 24, 545 (1898). Cf. also Fr. Kriiger: Z. Bioi. 

 26, 469 (1890), and Z. physiol. Chem. 25, 256 (1898). 



3 Cf. G. Hufner: ibid. 4, 382 (1880). 



4 G. Hufner and J. Otto: ibid. 7, 65 (1882); 8, 366 (1884). A. Jaderholm: Z. 

 Biol. 20, 419 (1884). 



5 Z. wiss. Zool. 14, 55 (1864). 



8 Cf. H. Molisch: Bot. Zeit. 1894, 177; 1895, 131. 



