n PRIMARY DISSOCIATION-PRODUCTS 41 



The ornithuric acid, according to E. Fischer, is also dextro-rotatory : 



a D = +7-85. 



On being heated with barium hydrate arginin becomes racemised 

 (see p. 91). The two arginins differ from one another as regards 

 polarisation, solubility, and shape of crystal. 1 Why fibrin yields much 

 larger quantities of r-arginin than do other albumins is not known. 1 



The occurrence of inactive arginin has also been observed by 

 Cathcart, 2 who subjected fibrin to ' urotryptic ' digestion, 3 and coagu- 

 lated serum to Hedin's spleen-enzyme : ' lieno-a-protease.' Cathcart 

 points out that the optically active arginine complex may become 

 racemised through the agency of the enzyme either before or after 

 liberation from the rest of the proteid molecule, analogous to the 

 partial racemisation of such compounds as atropine and amygdalin 

 under the katalytic action of weak alkali, or, that the arginin complex 

 of the proteid molecule is normally symmetrical and is liberated as 

 the inactive form by certain enzymes, while it is converted into the 

 optically active variety by the action of acids during the hydrolysis of 

 albuminous substances. 



Seemann's view as to how arginin is linked up in the albumin 

 molecule is given on pages 246 and 247. 



The part played by arginin in the metabolism of plants has been 

 investigated by E. Schulze and N. Castoro. 4 



14. Histidin, C 6 H 9 N 3 2 , was discovered by Kossel 5 as a dissocia- 

 tion-product of sturin, the protamin of the spermatic fluid of the 

 sturgeon, and also found by Hedin 6 in casein, egg-white, etc. 

 Since then it has been shown by Kossel 7 and his pupils, and by E. 

 Schulze, 8 to be a widely distributed dissociation-product. Except in 

 a few protamins, histidin has been found in all albumins hitherto 

 investigated. It is most abundant in globin, the albumin of haemo- 

 globin. It was first prepared by Kossel, 9 and again recently by 

 Frank el, 10 who used mercuric chloride as the precipitating agent ; later 



1 F. Kutscher, Zeitschr. f. physiol. Chem. 28. 88 (1899) ; 32. 476 (1901). 



2 E. P. Cathcart, Journ. of Physiol. 32. Proceedings XV. ; also p. 300 and Pro- 

 ceedings XXXIX. (1905). 



3 Urotrypsin is that proteolytic enzyme found in urine which digests in an alkaline 

 medium. See Cathcart's paper in Salkowski's Festschrift (1904). 



4 E. Schulze and N. Castoro, Zeitschr. f. physiol. Chem. 43. 170 (1904). 



5 A. Kossel, ibid. 22. 176 (1896). 



6 S. G. Hedin, ibid. 22. 191 (1896). 



7 See above under Arginin. 



8 S. Frankel, Sitzungsber. d. Akad. d. Wissensch. in Wien, mathem.-naturw. Kl. 

 112. Abt. II. 6 Marz 1903. 



