1 6 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



Bernard originally taught), or is employed in the synthesis of fat and proteid 

 (as Pavy holds). 



Dextrin is the name given to a number of intermediate substances 

 formed during the hydrolysis of starch ; the principal varieties are 

 erythrodextrin, which gives a red colour with iodine; achroodextrin, which 

 does not ; and maltodextrin, which has a lower molecular weight than 

 these. 1 The dextrins are dextrorotatory (maltodextrin has an (a) D = + 

 174 -5). They are soluble in water, and insoluble in alcohol and ether. 

 They give a blue solution with Trommer's test, but no reduction occurs 

 on boiling. 



Animal gum was discovered by Landwehr, 2 and resembles achroodextrin 

 and glycogen in some of its propertie^. It is a decomposition product of 

 mucin. When boiled with dilute sulphuric acid it yields a reducing but 

 unfermentable sugar. Animal gum, like the vegetable gums, gives gelatinous 

 precipitates with copper and iron salts. 



Animal dextran is a gummy material, secreted by the Schizoneura 

 lamiginosa, a gall-producing louse that attacks elms. 3 



Vegetable gums and mucilages include such substances as gum arabic, 

 wood gum, etc., which are of subordinate physiological interest. 



Cellulose is the name given to a number of carbohydrates which form 

 the chief constituent of vegetable cell walls. In old cells, where it 

 becomes very insoluble, it is called lignin. The celluloses are insoluble 

 in cold and hot water, in alcohol, ether, and dilute acids and alkalies. 

 A specific reagent for dissolving them is Schweitzer's reagent (a solution 

 of cupric hydrate in ammonia). 



With iodine and concentrated sulphuric acid they are turned blue ; 

 with nitric acid they yield nitroso-compounds of an explosive nature. 

 Prolonged treatment with strong mineral acids leads to the formation of 

 sugars ; in some cases glucose, in others mannose, is formed. Schulze's 

 inannoso-cellulose, 4 found in coffee and other seeds, is not a hemicellu- 

 lose (see next paragraph). The celluloses are not acted upon by the 

 digestive ferments proper ; but they may be broken up in the intestine 

 by bacteria into carbonic acid and methane. 



Hemicelluloses are those varieties of cellulose which differ from the others 

 by yielding monosaccharides by treatment with dilute mineral acids. The 

 hemicellulose of yellow lupins yields galactose and arabinose ; that of rye and 

 wheat, arabinose and xylose; that of certain nuts, mannose. 5 



Tunicin is animal cellulose. It is the chief constituent of the test or outer 

 investment of the turiicates. 6 



Cellulose has also been found in the animal kingdom in the skin of the 

 silkworm, 7 and in the zoocytium of Oplirydium versatile.^ 



Inosite. Inosite is a substance found in muscle and other animal 

 tissues, and in many vegetables also. Its crystalline form is shown 



1 Recent papers on dextrin will be found in Ber. d. deutsch. chem. Gesellsch., Berlin. 

 Bde. xxiii. S. 3060 ; xxvi. S. 2930 (by Scheibler and Mittelmeier), and Bd. xxvi. 8. 

 2533 (by Leubner and Doll). 



2 Ztschr.f. physiol. Chem., Strassburg, Bd. viii. S. 119, 124. 



3 Lieberraann, Arch. f. d. yes. Physiol. , Bonn, Bd. xl. S. 454. 



4 Ztschr. f. physiol. Chem., Strassburg, Bd. xvi. 



5 See Schulze, loc. cit. ; and Reiss, Ber. d. deutsch. chem. Gcsellsch., Berlin, Bd. xxii. 



6 Schafer, Ann. d. Chem., Leipzig, Bd. ccx. S. 312; Berthelot, Ann. dechim., Paris, 

 Se"r. 3, tome Ivi. p. 153. 



7 De Lucca, Compt. rend. Acad. d. sc. t Paris, tome lii. p. 102 ; Ivii. p. 43. 



8 Halliburton, Quart. Journ. Micr. Sc., London, July 1885. 



