THE VOLATILE PART OF PLANTS. 91 



EXP. 47. Prepare impure vegetable albumin from potatoes, cabbage, 

 or flour, as above described, and apply the nitrate of mercury test. 



As already intimated, albumin is chemically changed 

 or decomposed in the process of coagulation. Coagu- 

 lated albumin is not readily dissolved by dilute acids or 

 by dilute aqueous solutions of alkali. 



The so-called vegetable albumin is mostly known only 

 after coagulation by heat, and has been but imperfectly 

 studied. According to Ritthausen, the coagulum ob- 

 tained by heating the juice of potato tubers or the aque- 

 ous extracts of peas and horse-beans ( Vicia faba) is solu- 

 ble in dilute potash and in acetic acid; it is therefore 

 not albumin. Sidney Martin reports a genuine albumin 

 in the juice of the papaw, but its composition has not 

 been determined. 



Fibrin. Animal fibrin is insoluble in water, alco- 

 hol and salt-solutions : it swells up in dilute acids, dis- 

 solves in alkalies, and is coagulated by heat. 



The blood of the higher animals, when in the body or 

 when fresh drawn, is perfectly fluid. Shortly after it is 

 taken from the veins it partially solidifies it coagulates 

 or becomes clotted. It hereby separates into two por- 

 tions, a clear, pale-yellow liquid the serum and the 

 clot. As already stated, the serum contains albumin. 

 On persistently squeezing and washing the clot with 

 water, the coloring matter of the blood is removed, and 

 a white stringy mass remains, which consists chiefly of 

 fibrin, being a decomposition-product of another albu- 

 minoid, fibrinogen. 



In very dilute hydrochloric acid, fibrin swells up. but 

 does not dissolve. When freshly prepared, it absorbs 

 oxygen from the air and gives off carbon dioxide. Heat- 

 ing to 17G to 212 coagulates and shrinks it, and ren- 

 ders it less elastic and incapable of absorbing oxygen. 



Exr. 48. Observe the separation of blood into serum and clot : coag- 

 ulate the albumin of the former by lieat. and test it with warm hydro- 

 chloric acid. Tie up the clot in a piece of muslin, and squeeze and 



