CHEMICAL BASIS OF THE ANIMAL BODY. 101 



liberating from the cells the true food-stuffs which they contain. At 

 the same time the products formed during the solution of the cellulose 

 may, if they are oxidised in the body, contribute to its energy and thus 

 be of use 1 . 



7. Tunicin (C 6 H 10 O 8 ) W . 



This substance constitutes the chief part of the mantle of Tunicata 

 (Ascidians) and appears to have been first described by C. Schmidt 2 , 

 who drew attention to its similarity to vegetable cellulose. This view 

 was confirmed by Berthelot who however observed that it is much more 

 resistant to the action of acids than is true cellulose 3 . In other 

 respects the two may be regarded as identical. In accordance with 

 this it is found that tunicin is soluble in Schweizer's reagent (see 

 above), from which it may be reprecipitated by hydrochloric acid and 

 thus purified. It is further coloured blue by the addition of iodine 

 after preliminary treatment with sulphuric acid. It is soluble in 

 concentrated sulphuric acid, and if water be added to this solution 

 and it be boiled for some time, a sugar which is apparently identical 

 with ordinary dextrose is obtained 4 . 



It is prepared in the pure form by treating the mantles for some 

 days with water in a Papin's digester, then in succession with boiling 

 dilute hydrochloric acid, strong caustic potash and water. As thus 

 obtained it retains the form of the parent tissue. 



THE SUGARS. 



The researches of Emil Fischer have thrown a flood of light on the 

 chemistry of the sugars 5 . In phenyl-hydrazin (C 6 H 5 . NH . NH 2 ) he 

 discovered a reagent which forms with the sugars compounds known as 

 hydrazones and osazones. These provided for the first time by their 

 various solubilities, melting-points and rotatory powers an adequate 

 means of detecting, separating and characterising the several members 

 of this class of carbohydrates. Hence it became possible to investigate 

 the occurrence of sugars among the complicated products of the 

 reactions employed in the effort to effect their transformations and 



1 On the above see Weiske, Chem. Centralb. Bd. xv. (1884), S. 385. Henneberg 

 u. Stohmann, Zt. f. Biol. Bd. xxi. (1885), S. 613. Weiske (Eef.) Schulze u. 

 Flechsig, Ibid. xxn. S. 373. 



2 Liebig's Ann. Bd. LIV. (1845), S. 318. 



3 Ann. d. Ch. et Phys. 3 S6r. T. LVI. (1859), p. 149. 



4 Franchimont, Ber. d. d. chem. Gesell. 1879, S. 1938. Compt. Eend. T. LXXXIX. 

 (1879), p. 755. Schafer, Liebig's Ann. Bd. CLX. (1871), S. 312. 



5 Fischer has given a condensed account of his researches with full references to 

 the literature in Ber. d. d. chem. Gesell. Jahrg. xxm. (1890), S. 2114. Of this an 

 abstract is given in Jl. Chem. Soc. Nov. 1890, p. 1223. See also Schulz, Biol. 

 Centralb. Bd. x. (1890), Sn. 551, 620. 



