CHEMICAL BASIS OF THE ANIMAL BODY. 907 



Preparation. As a product of the decomposition of bile, and is purified by 

 removing any traces of bile acids by means of lead acetate, and then successively 

 crystallizing from water. 



Leucin. C 6 H 13 N0 2 . 



Is one of the principal products of the decomposition of nitrogenous matter, 

 either under the influence of putrefaction or of strong acids and alkalies. It occurs, 

 however, normally in the pancreas, spleen, thymus, thyroid, salivary glands, liver, 

 etc., and is one of the products of the tryptic (pancreatic) digestion of proteids; 

 in acute atrophy of the liver it is present in the urine in large quantity in company 

 with tyrosin. 



As usually obtained in an impure form it crystallizes in rounded lumps [Fig. 252], 

 which are often collected together and sometimes exhibit radiating striation. When 



[FiG. 252. 



Leucin Crystals.] 



pure, it forms very thin, white, glittering, flat crystals. These are easily soluble in 

 hot water,. less so in cold water and alcohol, insoluble in ether. They feel oily to 

 to the touch, and are without smell and taste. Acids and alkalies dissolve them 

 readily, and crystallizable compounds are formed. 



Carefully heated to 170 C. it sublimes, but at a higher temperature is decomposed, yielding 

 amylamin, carbonic anhydride, and ammonia. In the presence of putrefying animal matter it 

 splits up into valeric acid and ammonia. 



Leucin is amido-caproic acid, and may be represented thus : 



Preparation. From horn shavings by boiling with sulphuric acid, neutralizing 

 with baryta and separating from tyrosin by successive crystallization. See also 

 Kiihne, 1 who prepares it by the action of pancreatic ferment (trypsin) on proteids. 



Scherer has given the following test lor leucin. The suspected substance is 

 evaporated carefully to dryness with nitric acid ; the residue, if it is leucin, will be 

 almost transparent and turn yellow or brown on the addition of caustic soda. If 

 this be again very carefully concentrated with the alkali, an oily drop is obtained, 

 which is quite characteristic of this substance. Leucin, if not too impure, may be 

 easily recognized by its subliming on being heated ; a characteristic color of amyl- 

 amin is at the same time evolved. 



Asparagin. C 4 H 8 N 2 3 



Is not found as a constituent of the animal body, but appears to be formed by 

 the decomposition of proteids, notably during the germinative changes of the pro- 

 teids in leguminous seeds. 2 It is a crystalline body, and when boiled with acids or 

 alkalies is readily converted into aspartic acid. 



Aspartic (or asparaginic] Acid. C 4 H 7 NC 4 . 



This acid has been obtained in small quantities among the products of the pan- 

 creatic digestion of fibrin 3 and vegetable glutin, 4 although not occurring as a con- 



1 Virchow's Archiv, Bd. xxxix., S. 130. 



2 Landwirthski u. Versuchs Statioiien, Bd. xvii. 1. 



3 Radziejewski u. Salkowski. Ber. d. Deutsch. chem. Gesell., Jahrg. vii. (1874), S. 1050. 

 * V. Knieriem, Zeitschr. f. Biol.. Bd. xi. (1875), S. 198. 



