188 THE PRODUCTS OF ALBUMINOUS DIGESTION. 



variable size, which closely resemble globules of fat. In these, con- 

 centric striations, as well as very fine radiating lines, can at times be 

 made out on careful examination. 



Several leucins apparently exist. One form, which can be pro- 

 duced synthetically from hydrocyanic acid and ammonium-iso- 

 valerianic aldehyde, is optically inactive. The common leucin, 

 on the other hand, which is formed during tryptic digestion or on 

 decomposition of the native albumins with hydrochloric acid, is 

 dextrorotatory. A third form results from the action of Penicilium 

 glaucum upon the inactive substance, and is said to be laevorotatory. 

 According to Cohn, moreover, several isomeric, optically active 

 leucins exist. The common form is easily soluble in water, in 

 alkalies and acids, as also in hot alcohol ; in ether it is insoluble. 

 It combines with acids, alkalies, and the oxides of some of the heavy 

 metals to form salts. On boiling a solution of leucin with subacetate 

 of lead the corresponding compound of lead oxide can thus be 

 obtained if ammonia is carefully added to the cooled solution. A 

 copper salt is similarly formed if leucin in aqueous solution and con- 

 taining a small amount of alkali is treated with a solution of cupric 

 sulphate, care being taken not to add an excess. On standing, the 

 compound separates out in the form of clusters of blue needles, which 

 are characterized by their pronounced insolubility. 



When carefully heated to a temperature of 170 C. leucin melts 

 and sublimes in the form of white flakes, which are deposited on the 

 cooler portion of the tube. At the same time the odor of amylamin 

 develops. 



On evaporating a small amount of leucin upon platinum foil with 

 nitric acid a colorless residue is formed. If to this a drop of sodium 

 hydrate solution is added and heat is carefully applied, a yellowish 

 or brownish color develops, and on further heating an oil-like droplet 

 is obtained, which rolls about upon the platinum without adhering 

 (Scherer's test). 



On decomposition with an alkali or during the process of putre- 

 faction leucin yields ammonia and valerianic acid. On oxidation 

 leucinic acid results. 



As has been indicated, leucin is an amido-capronic acid of the 

 formula (CH 3 ) 2 .CH.CH 2 .CH(NH 2 ).COOH, and may hence also be 

 regarded as a-amido-isobutyl-acetic acid. 



Tyrosin. Tyrosin can be obtained on tryptic digestion from all 

 those albumins in which aromatic groups exist. Collagen, in which 

 this is absent, accordingly yields no tyrosin, and very small amounts 

 only are obtained from elastin. In the animal body it is practically 

 found as such only under pathological conditions if we disregard the 

 minute quantity which is formed in the intestinal canal. Like 

 leucin, it is also formed during the process of albuminous putrefaction, 

 and can be obtained artificially by decomposing albuminous sub- 

 stances with dilute mineral ncids or alkalies. 



While impure tyrosin may occur in the form of spherules similar 



