476 CHEMISTRY OF THE PROTEIDS CHAP. 



the blood is taken out of the tube and is put on ice. By this means 

 the addition of alcohol is reduced to a minimum. 



Schulz 1 prepares haemoglobin crystals by an entirely different 

 method, based on Hofmeister's principle of preparing crystals of 

 egg-albumin: the laked blood is mixed with an equal bulk of 

 saturated ammonium-sulphate solution to precipitate the globulins ; 

 in the filtrate the haemoglobin crystallises out and may then be 

 repeatedly recrystallised from half-saturated ammonium - sulphate 

 solutions. To prevent too rapid crystallisation, it is best to cool the 

 laked blood by placing it on ice, then to add ammonium-sulphate 

 solution, and finally to allow crystallisation to take place at the 

 ordinary room-temperature. Haemoglobin crystals prepared by this 

 method are large and well formed, but they contain ammonium 

 sulphate, which has to be removed by dialysis. According to Schulz 2 

 one is apt to get haemoglobin crystals along with serum-albumin 

 crystals if serum be employed which contains haemoglobin. 



According to Hoppe-Seyler the slightly soluble hemoglobins from 

 the blood of the dog, horse, guinea-pig, squirrel, and rat crystallise 

 readily, as does also the blood of the goose, duck, and pigeon. The 

 more soluble haemoglobins, e.g. those of man, ox, sheep, pig, and 

 rabbit, do not crystallise easily ; while the haemoglobins of the mouse, 

 mole, and bat crystallise somewhat more readily. The last blood 

 to be obtained in a crystalline form was that of the cat (Kriiger 3 and 

 Abderhalden 4 ). Further information regarding the haemoglobin 

 crystals of a large number of animals is given by Preyer ; 5 the literature 

 on blood crystals has been put together by Robert 6 and Schulz. 7 



For preparing haemoglobin crystals the blood of the dog or that of 

 the horse is most suitable ; pig's haemoglobin also crystallises readily 

 according to Otto, 8 although it is very soluble. 



It is much more difficult to make reduced haemoglobin crystallise, 

 as it is much more soluble. Kuhne 9 was the first to succeed, and 

 subsequently followed Gscheidlen, 10 Ewald, 11 Nencki, 12 Giirber, 13 and 



1 F. N. Schulz, Zeitschr. f. physiol. Chem. 24. 449 (1898). 



2 F. N. Schulz, Die Kristallisation von Mweissstoffen, Jena, Fischer, 1901. 



3 Fr. Kriiger, Zeitschr. f. Biologie, 26. 452 (1890) ; Zeitschr. f. physiol. Chem. 25. 

 256 (1898). 



4 E. Abderhalden, ibid. 24. 545 (1898). 5 W. Preyer, Blutkristalle, Jena, 1871. 



6 H. U. Kobert, Zeitschr. f. angewandte Mikroskopie, V. 6 to 10 (1900). 



7 F. N. Schulz, Die Kristallisation von Eiweissstoffen, Jena, Fischer, 1901. 



8 J. Otto, Zeitschr. f. physiol. Chem. 7. 57 (1882). 



9 W. Kiihne, Virchow's Archiv, 34. 423 (1865). 



10 R. Gscheidlen, Pftliger's Archiv f. d. ges. Physiol. 16. 421 (1878). 



11 A. Ewald, Zeitschr. f. Biologie, 22. 459 (1886). 



12 M. Nencki, Ber. d. deutsch. chem. Ges. 19. I. 28 and 410 (1886). 



13 Giirber, Sitzungsber. d. physik.-mediz. Ges. zu Wiirzburg, 1893 (Reprint). 



