148 LEUCIN. 



the addition of strong acetic acid. Hydantoin or methyl-hydantoiii 

 also yields the red colouration. 



2. Jaffe's reaction 1 . On the addition of an aqueous solution of 

 picric acid and a few drops of dilute caustic soda, an intense red 

 colouration is produced. This suffices to detect -1 part of kreatinin in 

 5000 of water. Acetone alone gives a similar colouration but to a 

 comparatively very feeble extent. 



By prolonged boiling of kreatinin with Fehling's fluid, reduction 

 takes place but there is no simultaneous separation of cuprous oxide, 

 and it appears that kreatinin may prevent the separation of the oxide 

 when the reduction is due not to itself but to such a substance as 

 dextrose 2 . 



6. Leucin. C 6 H 13 N0 2 . [CH 3 . (CH 2 ) 3 CH (NH 2 ) COOH]. 

 (a-Amido-caproic acid). 



Is a characteristic product of the decomposition of proteids and 

 gelatin whether by the action of boiling acids, caustic alkalis or 

 putrefactive influences. It occurs normally in variable amounts in 

 the pancreas, spleen, thymus, thyroid, salivary glands, liver &c. and 

 also in plants, more especially in those parts in which reserve materials 

 are accumulated, such as bulbs, tubers and seeds. It is also typically 

 formed during the tryptic (pancreatic) digestion of proteids to an extent 

 which amounts on the average 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 conditions of the liver is by no means so constant or certain 

 as it presumably 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 3 . 



As usually obtained in a more or less impure form it crystallises 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 Isevorotatory, acid and alkaline 

 solutions on the other hand dextrorotatory. 



1 Zt. f. physiol Chem. Ed. x. (1886), S. 399. 



2 Worm Miiller, Pfliiger's Arch. Bd. xxvn. (1882), S. 59. 



3 Cf. Salkowski, Die Lehre vom Harn, 1882, S. 427. Lea, Jl. of Physiol. Vol. 

 xi. (1890), p. 258. 



