58 H^lMATOGEN. THE ALBUMINOIDS. 



which contain iron are important from their being probably the 

 origin of the animal iron compounds. 



H^IMATOGEN. 



135. Prepare from the yelk of an egg. Shake the yelk in 

 a wide-mouth, glass-stoppered bottle with two or three times its 

 volume of alcohol; allow it to stand and when it has settled pour 

 off the alcohol. Repeat this operation twice, then extract in the 

 same manner, or, better, in an extraction apparatus with ether 

 until the residue is white. Digest this in artificial gastric juice 

 (made as in Experiment 133). The nuclein, haematogen, remains. 



136. Dissolve a portion in ammonia. Test for iron by 

 ammonium sulphid. At first there is no color, but after a time 

 the solution turns greenish and, in twenty-four hours, black, as 

 the iron is gradually set free from the compound. In the same 

 manner test with potassium ferrocyanid. The Prussian blue is 

 formed slowly, differing thus from its production with the ordi- 

 nary iron salts. 



137. Add to the nuclein some hydrochloric acid, then, after 

 neutralizing with ammonia, test for iron as before. The acid has 

 decomposed the nuclein, so that the tests are obtained imme- 

 diately. 



THE ALBUMINOIDS. 



The albuminoids are found in the insoluble form, 

 mostly in the bones of the body or the parts which are 

 used for protection. They resemble the albuminous sub- 

 stances, giving many of the same products when they are 

 decomposed, differing, however, in other respects. They 

 are not easily attacked by the reagents which dissolve and 

 decompose albuminous compounds. Only the collagen and 

 its derivative, gelatin, with possibly elastin, are digestible. 



COLLAGEN. 



This substance is found in the animal body in the 

 connective and cartilaginous tissues, tendons, and bones. 



