164 CHEMISTRY OF THE PROTEIDS CHAP. 



2. The second reason has already been given on p. 67. If, after 

 deducting the water, one adds together the carbon, nitrogen, 

 and oxygen values of the known dissociation-products of globin, 

 figures are obtained with a higher value for carbon and nitrogen 

 and a lower value for oxygen than are possessed by the mother- 

 substance, namely globin. Therefore the most ready ex- 

 planation seems to be that one or more carbohydrate groups 

 are contained in the unknown radical (Cohnheim). 

 Mucins and egg -albumin are therefore not glyco-proteids in the 

 sense that compounds of nucleic acid with albumins are nucleo-proteids, 

 for they only contain one of the usually occurring dissociation-products 

 in a larger or in a more readily accessible amount. Some albumins 

 e.g. casein, gelatine, and elastine do not seem to possess any carbo- 

 hydrate, and are in this respect analogous to other compounds in 

 which, e.g., the glycocoll or ty rosin radicals are absent. 



In what form carbohydrates are contained in the albumins we 

 therefore do not know ; we can only say that glucosamin is derived 

 from it secondarily. 



SOME PHYSIOLOGICAL CONSIDERATIONS 



As in cases of diabetes mellitus, the amount of sugar found in the 

 urine is far in excess of the amount of glucosamin occurring normally 

 in the albumin-molecule (see p. 161). Miiller, Kossel, Kraus, 1 and 

 R. Cohn have developed the conception that carbohydrate may be 

 formed out of certain atomic complexes which themselves do not 

 possess a carbohydrate nature. These investigators have assumed 

 that the hexone-bases (see p. 20) or that amino-acids, set free by 

 the dissociating action of pepsin, trypsin, and erepsin may become 

 des-aminated ; that their carbon-chain may be broken up and then be 

 reformed into carbohydrates. 



That di-amino-propionic acid is of special interest in connection 

 with the formation of carbo-hydrates out of albumins has been pointed 

 out by Paul Mayer. 2 (See below.) 



Klebs, the discoverer of di-amino-propionic acid, 3 showed that this 

 acid is converted into e'-glyceric acid on being acted upon by gaseous 

 nitrous acid. With the view of removing only one NH 2 - radical, 

 Neuberg and Silbermann 4 added an equivalent amount of silver nitrite 



1 Fr. Kraus, Berlin, klin. Wochensch. No. 1 (1904). (Here is given a summary 01 

 the literature.) 



2 P. Mayer, Zeitschr. f. physiol. Chem. 42. 59 (1904). 



3 0. Klebs, ibid. 19. 301 (1894). 



4 C. Neuberg and M. Silbermann, Ber. d. deutsch. chem. Ges. 37. 341 (1904). 



