72 PHYSIOLOGICAL CHEMISTRY. 



the blood solution to evaporate in an open dish in the air, cool the 

 filtered blood solution to C., add while stirring vol. of alcohol 

 also cooled, and allow to stand a few days at 5 to 10 C. 

 The crystals which separate may be repeatedly recrystallized by dis- 

 solving in water of about 35 C, cooling and adding cooled alcohol 

 as above. Lastly, they are washed with cooled water containing 

 alcohol (i vol. alcohol) and dried in vacuum at 0. or a lower 

 temperature. According to GSCHEIDLEN'S investigations, oxy- 

 haemoglobin crystals may be obtained from difficulty crystallizable 

 varieties of blood by allowing the blood first to putrify slightly 

 in sealed tubes. After shaking with air by which the blood is 

 again arterialized, proceed as above. 



For the preparation of oxyhaemoglobin crystals in small quanti- 

 ties from blood easily crystallized, it is often sufficient to stir a 

 drop of blood with a little water on a microscope slide and allow the 

 mixture to evaporate so that the drop is surrounded by a dried ring. 

 After covering with a thin glass, the crystals gradually appear radiat- 

 ing from the ring. These crystals are formed in a surer manner if 

 the blood is first mixed with some water in a test-tube and shaken 

 with ether and a drop of the lower deep-colored liquid treated as 

 above on the slide. 



Haemoglobin, also called KEDUCED HAEMOGLOBIN or PURPLE 

 CRUORIN (STOKES), occurs only in very small quantities in arterial 

 blood, in larger quantities in venous blood, and is nearly the only 

 blood-coloring matter after suffocation. 



Haemoglobin is much more soluble than the oxyhaemoglobin, and 

 it can therefore only be obtained as crystals with difficulty. These 

 crystals are as a rule isomorphous to the corresponding oxyhaemo- 

 globin crystals, but are darker, having a shade towards the blue or 

 purple, and are decidedly more pleochromatic. Its solutions in 

 water are darker and more violet or purplish than solutions of oxy- 

 haemoglobin of the same concentration. They absorb the blue and 

 the violet rays of the spectrum in a less marked degree, but strongly 

 absorb the rays lying between C and D. In proper dilution the 

 solution shows a spectrum with one broad, not sharply-defined band 

 between D and E. This band does not lie in the middle between 

 D and E, but is towards the red end of the spectrum, a little over 

 the line D. A haemoglobin solution actively absorbs oxygen from 

 the air and is converted into an oxyhaemoglobin solution. 



A solution of oxyhaemoglobin may be easily converted into a 

 haemoglobin solution by means of a vacuum, by passing an indiffer- 



