722 PROTEIDS. [Apr. 



&c., have also been obtained; also by tryptic digestion, hypoxanthin 

 and perhaps xanthin. But urea has never yet been derived by direct 

 decomposition from proteid material, the statements to this effect 

 having been based on errors. In spite of numerous researches, we 

 cannot at present state definitely what is the real constitution of 

 a proteid, or in what manner these several residues are contained in the 

 undecomposed substance. It is unnecessary to give here any of 

 the formulae, nearly all empirical, which have been made to represent 

 a proteid ; they all give with equal exactitude the percentage compo- 

 sition, but beyond this they are untrustworthy. Of the various attempts 

 which have been made to assign to proteids some definite molecular 

 structure, none appear, at the present stage of information, sufficiently 

 reliable for general acceptance. 



Among the most elaborate labours in this direction may be mentioned tbose of 

 Hlasiwetz and Haberman. In their first publication 1 , starting from the general 

 similarity of the products of decomposition of the proteids and carbohydrates, they 

 tried to establish a definite relation between the two classes of bodies. In this they 

 were not successful, and in their second research 2 they come to the conclusion 

 that the carbohydrates take no part in the formation of the proteids. 



Other experiments in the same direction have been made by Scliiitzenberger 3 . He 

 shews that albumin can be decomposed into carbonic anhydride and ammonia, and 

 that the ratio of these two is the same as though urea had been the body on which 

 he operated. From this he concludes that "the molecule of albumin contains the 

 grouping of urea and represents a complex ureide." In his second publication 4 he 

 confirms his previous results, stating that the ammonia, carbonic anhydride and 

 oxalic acid, produced by the decomposition of proteids, are so connected quanti- 

 tatively as to be capable of derivation from varying proportions of urea and oxamide. 

 He also obtained from the decomposition of proteids a nitrogenous residue which 

 could be formulated as giving rise to all the amidated acids and other bodies spoken 

 of above. Thus according to him, albumin, built up as a complex ureide, decomposes 

 into ammonia, carbonic, oxalic, and acetic acids, and this nitrogenous body : this 

 last then gives rise to the other products of decomposition 5 . 



It will be noticed that in the general description of the various 

 proteids, distinctive reactions for each could not be given, but that 

 varying solubilities were the chief means at our disposal for distinguishing 

 them. They may be arranged according to their solubilities in the 

 following tabular form. 



Soluble in distilled water : 



Aqueous solution not coagulated on boiling Peptones. 



Aqueous solution coagulated on boiling Albumins. 



1 Ann. d. Chem. u. Pharm. Bd. 159, S. 304. 



2 Ibid. Bd. 169, S. 150. 



3 Comptes Rendus, T. 80 (1875), p. 232. Bull, de la Soc. chim. xxin. 161, 193, 

 216, 242, 385, 433, xxiv. 2 et 145. 



4 Compt. Rend. T. 81, p. 1108. Bull de la Soc. chim. xxv. 147. 



6 See also Schutzenberger, Ann. de Chem. et de Phys. T. xvi. (1879), p. 280. 



