CHEMICAL BASIS OF THE ANIMAL BODY. 1245 



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. Leucine is particu- 

 larly soluble in presence of acids and alkalis. The aqueous solu- 

 tions are lsevorotatory, 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, (ii) From the products of 

 the 2^'olonged tryptic (pancreatic) digestion of proteids. 



For ordinary practical purposes the microscopic appearance 

 of the crystals affords the most convenient means for recognizing 

 leucine, and in this way very minute traces may be determined 

 with certainty. The confirmation of the clue thus afforded by 

 the application of chemical tests is however not easy unless a 

 fair amount of material is at hand, and that in a pure condition. 

 When carefully heated to 170° leucine sublimes and yields a 

 characteristic odour of amylamine. 



8. Lysine. C 6 H 14 N 2 2 . [C 5 H 9 (NH 2 ) 2 . COOH]. (Di- 

 amido-caproic acid.) 



This base has been recently discovered among the crystalline 

 products formed when casein is decomposed by being boiled 

 with hydrochloric acid and stannous chloride under exclusion 

 of oxygen. It may be separated from the mother liquor as a 

 double salt with platinum chloride. It may be separated from 

 this salt as a hydrochloride by the action of sulphuretted hydro- 

 gen, and from the hydrochloride it is obtained in the free state 

 by boiling with hydroxide of lead. As thus obtained it is 

 optically active, being dextrorotatory, but by heating to 150° in 

 presence of baryta it becomes inactive. 



Further investigation has shewn that lysine may be simi- 

 larly formed by the decomposition of egg-albumin, gelatin and 

 keratin. It has also been found among the products of a pan- 

 creatic digestion of proteids (fibrin). 



9. Taurine. C 2 H 7 NS0 3 . [CH 2 (NH 2 ) . CH 2 (S0 2 .OH)]. 



(Amido-ethylsulphonic acid. ) 



Isethionic acid, CH 2 (OH) . CH 2 . S0 2 (OH), like glycolic 

 acid, CH 2 (OH) . COOH, contains two hydroxyls replaceable 

 by amidogen NH 2 , so that two isomeric amido-derivatives can 

 be formed from it. Of these one is amido-isethionic acid, 

 CH 2 (OH). CH 2 . S0 2 (NH 2 ), the other amido-ethylsulphonic 

 acid or taurine. 



