540 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Alcohols containing More than Five Carbon Atoms. 



Of these, cetyl alcohol, C„dl,,< )II. is found combined with palmitic acid in spermaceti; 

 cerotyl alcohol^ C., 7 II <MI . is found as an ester in Chinese wax; and melicyl alcohol, 

 CsqHqOH, is combined with palmitic acid in beeswax. 



Acids containing More than Five Carbon Atoms. 



Caproic Acid, C s H M COOH. — This is formed from the putrefaction of 

 proteidj being found in cheese and in feces j it may likewise be detected in the 

 sweat. United with glycerin it occurs in butter-fat. 



Iso-butyl Amido-acetic Acid, or Leucin, (CH 3 ) 2 : CH.CH 2 .CHNH 2 . 

 COOH. — This substance is a constant product of proteid putrefaction, is there- 

 fore found in cheese, and may likewise be obtained by boiling proteid or gelatin 

 with sulphuric acid or with alkali. When fed it is converted into urea. When 

 fed to birds the tissues decompose it with elimination of ammonia, which latter 

 may be converted into uric acid by the liver. 1 It is said to occur in pancreatic 

 juice. According to Kiihne it is produced in trypsin proteolysis to the extent 

 of 9.1 per cent, of the proteid used. Since this weakly alkaline medium in 

 pancreatic digestion is especially favorable to bacterial activity, Kiihne added 

 antiseptic salicylate of sodium and still found leucin (and tyrosin). The same 

 results are obtained with thymol. It is generally accepted that leucin (and 

 tyr< >sin) are normal products of tryptic digestion. In certain diseases of the liver 

 leucin (and tyrosin) appear in the urine, which may be interpreted to mean that 

 these substances, normally produced from proteid metabolism in the tissues, are 

 not normally burned but accumulate within the body, and are excreted (see 

 below). Proteid on chemical treatment may yield as much as 50 per cent, 

 of leucin. Since leucin contains six atoms of carbon it has been suggested 

 by Fr. Miiller that this substance and other proteid cleavage products con- 

 taining six carbon atoms may be the mother substances of the sugar produced 

 in diabetes. Cohn 2 asserts that feeding leucin to rabbits will increase the 

 glycogen in their livers, but this increase is very slight. But Halsey 3 shows 

 that there is no increase in sugar in the urine after feeding leucin in diabetes. 

 It may be that a sugar radicle in proteid may be the mother-substance of 

 leucin (see p. 581). 



Leucin and tyrosin are found in yellow atrophy of the liver both in the urine and in 

 the liver itself, under conditions indicating their production by bacteria and their non- 

 combustion after production. In phosphorus-poisoning and acute anaemia leucin and 

 tyrosin occur in the urine, but apparently without good ground for considering them of 

 bacterial oriuin. 



Leucin crystallizes in characteristic hall-shaped crystals. It was formerly supposed to 

 be amido-caproic acid, but Schulze 4 has shown its true composition. Inactive leucin con- 

 - 3tfi of a mixture of </- and /-leucin. and maybe obtained by treating conglutin with 



1 Minkowski: Archiv fur at/per. Palhologie unci Pharmakotogie, 1886, lid. 21, S. 85. 



-' Zeitschnft fiir physiologische Chemie, 1899, Bd. 28, S. 211. 



nng8berichte der Oesellschqfi zur Befdrderung der gesammten Naturwissenschaften zu Marburg, 

 1899, >. 102. 



1 Berichte der deutschen chemischen OeselUchaft, 1891, Bd. 24, S. 669 ; also, Gmelin: Zeitxchrift 

 fiir physiologische Chemie, 1893, Bd. 18, S. 38. 



