CHEMICAL BASIS OF THE ANIMAL BODY. 883 



from semen, from the nuclei of the red blood-corpuscles of birds and amphibia, 

 from hepatic cells, and it is probably present in all nuclei. 



When newly prepared it is a colorless amorphous body, soluble to a slight ex- 

 tent in water, readily soluble in many alkaline solutions ; but its solubilities alter on 

 keeping. If added gradually in sufficient quantity to a solution of caustic alkali 

 it first neutralizes the solution and then renders it acid. It seems to possess an 

 indistinct xantho-prpteic reaction, but gives no reaction with Millon's fluid. It 

 yields precipitates with several salts, e. g. , zinc chloride, argentic nitrate, and cupric 

 sulphate. 



Preparation. 1 Since nuclein is very resistant to the action of pepsin, it may be 

 obtained from the granular residue consisting chiefly of nuclei, which occurs after 

 digesting pus with pepsin. The most remarkable feature of this body is its large 

 percentage of phosphorus, 9.59 per cent. This phosphorus is readily separated 

 by boiling \yith strong hydrochloric acid or caustic alkalies ; the same occurs when 

 solutions of nuclein are acidulated and allowed to stand. 



Chitin. C 13 H 26 N 2 



10- 



Although not found as a constituent of any mammalian tissue, this substance 

 composes the chief part of the exo-skeleton of many invertebrates. It may 

 probably be regarded as the animal analogue of the cellulose of plants, and from 

 this point of view it possesses considerable morphological interest. Both cellulose 

 and chitin appear to yield some form of sugar when treated with strong acids. 



When purified, chitin is a white amorphous body, often retaining the shape of 

 the tissue from which it has been prepared. It is insoluble in all reagents except 

 strong mineral acids, the best solvents being sulphuric or hydrochloric acids. The 

 immediate addition of water to these solutions reprecipitates the chitin in an un- 

 altered form ; but the prolonged action of sulphuric acid causes a decomposition 

 resulting, according to some observers, in the formation of an amorphous ferment- 

 able carbohydrate ; and when hydrochloric acid is used an amidated carbohydrate 

 is obtained to which the name of glycosamin 3 (C 6 H ]3 N0 5 ) has been given. 



Preparation.* The cleansed exo-skeleton of a lobster is thoroughly extracted 

 with dilute hydrochloric acid and then with caustic soda. To purify it finally it is 

 submitted to prolonged boiling with a solution of potassic permanganate. 



[Nucleo-albumin. 



This term is applied to a class of substances which seem to be composed of 

 nuclein and an albuminous proteid. Casein is probably a nucleo-albumin, for when 

 subjected to peptic digestion a residue of nuclein is obtained.] 



CARBOHYDRATES. 



Certain members only of this class occur in the human body ; of these the most 

 important and widespread are those known as glycogen and the two sugars, grape- 

 sugar or dextrose (glucose), with which diabetic sugar seems to be identical, 5 and 

 maltose. Next to these comes milk-sugar. Inosit is another body of this class, 

 although it differs in many important points from the preceding two. 



Sugars are often considered to be polyatomic alcohol. Several of them stand in peculiar rela- 

 tion to mannit, and may be converted into that substance by the action of sodium amalgam. 6 



[When solutions of sugars are warmed in the presence of phenyl-hydrazin and 

 dilute acetic acid, amorphous or crystalline substances separate, which are termed 

 osazones. These differ according to the different sugars.] 



1. Dextrose (grape-sugar). C 6 H 12 6 +H,0. 



Occurs in the contents of the alimentary canal to a variable extent dependent 

 on the nature of the food taken. It is also a normal constituent of blood, chyle, 

 and lymph. Concerning its presence in the liver, see p. 538. The amniotic fluid 



1 See Kossel, Zeitschr. f. physiol. Chem., Bd. iii. (1879), S. 284 ; iv. (1880), S. 290 ; vii. (1883), S. 7. 

 " Untersuch. iiber d. Nuclein u. ihre Spaltungsprod, Strassb., 1881. 



2 Ledderhose. Zeitschr. f. physiol. Chem., Bd. ii. (1878), S. 213. 



3 Ledderhose, loc. cit., Bd. iv. (1880), S. 139. 



4 Biitschli, Arch. f. Anat. u. Physiol., Jahrg., 1874, S. 362. 



6 The question, however, whether several varieties of sugar occurring in the animal body have 

 not been confounded together under the common name of dextrose or glucose maybe consid- 

 ered at present an open one. 



6 Linnemann, Ann. d. Chem. u. Pharm., Bd. cxxiii., S. 136. 



