CHEMICAL BASIS OF THE ANIMAL BODY. 879 



into sugar : this latter is one of the crucial tests for a true member of the carbo- 

 hydrate group. According to Heschl 1 and Cornil, 2 anilin-violet (methyl-anilin) 

 colors lardaceous tissue rosy red, but sound tissue blue. 



The colors mentioned above as being produced by iodine and sulphuric acid are much clearer 

 and brighter when the reagents are applied to the purified lardacein. When the reagents are 

 applied to the crude substance in its normal position in the tissues, the colors obtained are always 

 dark and dirty looking. 



Purified lardacein is readily soluble in moderately dilute ammonia, and can. by 

 evaporation, be obtained from this solution in the form of tough, gelatinous fiakes 

 and lumps ; in this form it gives feeble reactions only with iodine. If the excess 

 of ammonia is expelled, the solution becomes neutral, and is precipitated by dilute 

 acids. 



Preparation. The gland or other tissue containing this body is cut up into small 

 pieces, and as much as possible of the surrounding tissue removed. The pieces are 

 then extracted several times with water and dilute alcohol, and if not thus rendered 

 colorless are repeatedly boiled with alcohol containing hydrochloric acid. The 

 residue after this operation is digested at 40 C., with good artificial gastric juice in 

 excess. Everything, except lardacein and small quantities of mucin, nuclein, 

 keratin, together with some portion of the elastic tissue, will thus be dissolved and 

 removed. 3 From the latter impurities it may be separated by decantation of the 

 finely-powdered substance. 



The chief products of the decomposition of proteids are ammonia, carbonic 

 anhydride, leucin, and tyrosin. Several other bodies, for the most part, like leucin, 

 amidated acids, such as aspartic acid, glutamic acid, etc. , 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 

 composition, 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 accept- 

 ance. 



Among the most elaborate labors in this direction may be mentioned those of Hlasiwetz and 

 Haberman. In their first publication, 4 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 5 they 

 came 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 Schiitzenberger.e He shows that 

 albumin can be decomposed into carbonic anhydride and ammonia, and thai 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 7 he confirms his previous results, stating that the ammonia, carbonic anhy- 

 dride, and oxalic acid, produced by the decomposition of proteids, are so connected quantitatively 

 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 xireide, decomposes into ammonia, carbonic, oxalic, and acetic acids, and 

 this nitrogenous body ; this last then gives rise to the other products of decomposition. 8 



It will be noticed that in the general description of the various proteids distinc- 

 tive 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: 



1 Wien. med. Wochenschr., No. 32, S. 714. 



2 Compt. Rend., T. Ixxx. (1875), p. 1288. 



3 Kiihne und Rudneff, Virchow's Archiv, Bd. xxxiii. (1865), S. 66. 



4 Ann. d. Chem. u. Pharm., Bd. clix. S. 304. 5 ibid., Bd. clxix. S. 150. 



e Comptes Reridus, T. Ixxx. (1875), p. 232. Bull, de la Soc. Chim. xxiii., 161. 193, 216, 242, 385, 

 483, xxiv.2et!45. 



7 Comptes Rendus, T. Ixxxi. p. 1108. Bull, de la Soc. Chim. xxv. 147. 



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



