348 LEUCIK 



to some 8 10 p. c. on the proteid digested, and is in this case 

 always accompanied by tyrosin. It may occur in the urine, more 

 particularly in cases of acute yellow atrophy of the liver ; but its 

 presence in this excretion in other and more general diseased con- 

 ditions of the liver is by no means so constant or certain as it pre- 

 sumably would be on the common assumption that a large part of 

 the urea leaving the body is due to its formation from leucin under 

 the converting action of the liver. 1 



As usually obtained in a more or less impure form it crystal- 

 lises in rounded fatty-looking lumps which are often collected 

 together and sometimes exhibit radiating striation. When pure, 

 it forms very thin, white, glittering flat crystals. It is extremely 

 soluble in hot water, less so but still very soluble in cold water, 

 soluble in alcohol, insoluble in ether. The crystals feel oily to the 

 touch, and are without smell and taste. Leucin is particularly 

 soluble in presence of acids and alkalis. The aqueous solutions 

 are laevorotatory, acid and alkaline solutions on the other hand 

 dextrorotatory. 



Preparation, (i) From horn shavings by prolonged boiling 

 with sulphuric acid, 5 of acid to 13 of water. The resulting 



FIG. 12. LEUCIN CRYSTALS. (Krukenberg.) 



fluid is neutralised by baryta and filtered, the excess of baryta 

 removed by the cautious addition of dilute sulphuric acid, and 

 the final filtrate concentrated to crystallisation. It is separated 

 from tyrosin by repeated crystallisation, taking advantage of the 

 great solubility of leucin and the slight solubility of tyrosin. 

 (ii) From the products of the tryptic (pancreatic) digestion of 

 proteids. After prolonged digestion, using thymol and salicylic 

 acid to prevent putrefaction, the fluid is filtered, moderately con- 

 centrated, and set aside to crystallise ; by this means a large part 



1 Cf. Salkowski, Die Lehre vom Ham, 1882, S. 427. Lea. Jl. of Phusiol. Vol. 

 xi. (1890), p. 258. 



