106 CHEMISTRY OF THE PROTEIDS CHAP. 



were obtained. In what amounts any acid will be found depends 

 primarily on the stage which germination has reached in a plant. 



Of especial importance are finally the investigations into the nature 

 of tyrosinase, which were made by Bertrand, 1 Gonnermann, 2 and 

 others. This tyrosinase is a ferment which is liberated in dying 

 vegetable cells ; it converts tyrosin into homogentisinic acid, and 

 causes thereby the blackening or darkening of beetroot juice, of cuts 

 into plants, etc. Biedermann, 3 v. Fiirth and Schneider, 4 and Przi- 

 bram 4 have also demonstrated the presence of tyrosinase in animals, 

 e.g. in the secretion of the midgut of the mealworm, 3 in the hsemo- 

 lymph of butterflies, and in the ink- sac of sepia. 5 It converts, 

 according to v. Fiirth and Schneider, tyrosin, but also pyrocatechin, 

 hydroquinone, suprarenin, and oxyphenylethylamin, into dark bodies, 

 which in their behaviour closely resemble the melanins. These dark 

 bodies, and also melanin, are produced as the result of oxidation. 

 Ducceschi 4 succeeded also in changing tyrosin into darkly coloured 

 bodies by means of careful oxidation with chlorates. See also p. 580, 

 chapter XII. 



3. Disintegration during the Metabolism of Animals. The changes 

 which nucleo-proteids undergo as the result of auto-digestion are dealt 

 with later. See p. 431. 



The albumin, taken as food, is converted in the alimentary canal 

 of the higher animals by means of the four proteolytic ferments, pepsin, 

 trypsin, erepsin, and arginase, into primary crystalline dissociation- 

 products, the ammo-acids, etc., which are then absorbed in this form. 5 

 Whether a part of the albumin taken as food can or cannot be 

 absorbed in the form of albumoses, peptones, and peptids, is a question 

 which has not yet been settled, 6 and which cannot be discussed here. 



Aromatic amino-acids have been specially studied by the following 

 investigators : 



E. and H. Salkowski 7 believed that non-aminated acids which are 



1 Bertrand, Compt. rend. 122. 1215 (1896); vgl. H. Steudel, Deutsche med. 

 Wochenschr. 1900, p. 372. 



2 M. Gonnermann, Pfliiger's Arch. f. d. ges. Physiol 82. 289 (1900). 



3 W. Biedermann, ibid. 72. 105 (1898). 



4 0. v. Fiirth and H. Schneider, Hofmeister's JBeitrage, 1. 229 (1901). 



5 A. Schmidt-Mulheim, Arch. f. (Anat. u.) Physiol. 1879, p. 39 ; 0. Cohuheim, 

 Zeitschr. f. physiol. Ghem. 35. 396 (1902), 36. 13 (1902) ; F. Kutscher and J. See- 

 mann, ibid. 34. 528 (1902) ; 0. Lowi, Arch.f. experiment. Pathol. u. Pharmakol. 48. 

 305 (1902). 



6 E. Fischer and E. Abderhalden, Zeitschr. f. physiol. Ghem. 39. 81 (1903) ; G. 

 Embden and F. Knoop, Hofmeister's Beitr. 3. 120 (1902). 



7 E. and H. Salkowski, Zeitschr. f. physiol. Chem. 7. 169 (1883). 





