232 LEUCINE. [BOOK n. 



(2) CH 3 (CH 2 ) 3 CH(NH 2 )COOH 



a-Amidonormal caproic acid. 



= CH3(CH 2 ) 3 CH(OH)COOH + N 2 + H 2 0. 



Oxycaproic or leucic acid. 



2ndly. When heated with barium hydrate, the amido-acids split 

 up into alcohol bases and carbon dioxide. Thus : 



CH 2 (NH 2 )COOH = CH 3 NH 2 + C0 2 . 



Glycocine. Methylamine. 



To conclude these few very elementary observations on the 

 amido-acids, it may be remarked that these bodies in virtue, firstly, 

 of the acid carboxyl-group, and secondly of the basic amido-group 

 which they contain, are at once acids and bases, combining both with 

 bases and acids to form salt-like compounds. 



Leucine 



CH 3 CH, 

 (a-amido-isobutylacetic acid CH-CH 2 -CH(NH 2 )COOH.) 



Occurrence Leucine has been found in several of the tissues and 



in the organ- organs, especially of the glands, of the healthy body : 

 in the spleen, the thymus, the thyroid, in the parotid 

 and submaxillary glands, and above all in the pancreas. It is to the 

 eminent pathologist Virchow 2 that the merit belongs of having first 

 discovered leucine and tyrosine as non-pathological constituents of 

 the pancreas, both in man and the lower animals. He pointed out, 

 further, that the proximate principle which Scherer had separated 

 from the spleen and called lienin was undoubtedly leucine. 

 Virchow's short and apparently forgotten paper is of great interest 

 in connection with the history of discoveries in pancreatic digestion. 

 Scherer 3 separated from 20 pounds of the pancreas of the ox, 180 

 grammes of pure leucine, an amount which corresponds to 1*77 per 

 cent, of the fresh, and to 7 '37 per cent, of the dried and water-free 

 glandular tissue. At the time when Scherer analysed the pancreas, 

 the discovery afterwards due to Kuhne had not been made, viz. that 

 trypsin, as a result of its digestive activity, splits up the albuminous 

 bodies, and that amongst the most obvious and best characterised 

 products are leucine and tyrosine : further that, as the result of a 

 process of auto-digestion, the gland soon after death is found to 

 contain such considerable quantities of these amido-acids as were 



1 Leucine (from Xeu/cos, bright, clear, white) owes its name to its discoverer, 

 Braconnot, who probably wished to emphasize the origin of the colourless crystals 

 which he had obtained from the black charred products resulting from the action of 

 boiling sulphuric acid on muscle. 



2 Rud. Virchow, ' Zur Chemie des Pancreas.' Virchow's Archiv, Vol. vn. (1854), 

 p. 580. 



3 Scherer, Liebig's Annalen, Vol. cxn., p. 257. 



