728 CARBOHYDRATES. [App. 



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 solu- 

 tions reprecipitates the chitin in an unaltered form ; but the prolonged 

 action of sulphuric acid causes a decomposition resulting, according to 

 some observers, in the formation of an amorphous fermentible carbo- 

 hydrate ; and when hydrochloric acid is used an amidated carbohydrate 

 is obtained to which the name of glycosamin l has been given. 



Preparation 2 . The cleaned exoskeleton 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. 



CARBOHYDRATES. 



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

 these, the most important and wide-spread are those known as glycogen 

 and the two sugars, grape-sugar or dextrose (glucose), with which 

 diabetic sugar seems to be identical 3 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 alcohols. Several of them 

 stand in peculiar relation to mannit, and may be converted into that substance by 

 the action of sodium amalgam 4 . 



1. Dextrose (Grape-sugar). C 6 H 12 O 6 + H 2 O. 



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 con- 

 stituent of blood, chyle,- and lymph. Concerning its presence in the 

 liver, see p. 419. The amniotic fluid also contains this body. Bile 

 in the normal condition is free from sugar, so also is urine, though 

 this point has given rise to great dispute 5 . The disease diabetes is 

 characterized by an excess of dextrose in the fluids and tissues of the 

 body (see p. 424). 



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



2 Biitschli, Arch. f. Anat. u. Phijsiol. Jahrg. 1874, S. 362. 



3 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 may be considered at present an open one. 



4 Linnemann, Ann. d. Chem. u. Pharm. Bd. 123, S. 136. 

 6 See Seegen, Der Diabetes Mellitus, 2 Ed. S. 196. 



