110 CANE-SUGAR. 



(iii) Seidel's reaction. 1 A small amount (say -03 gr.) of the 

 suspected substance is evaporated to dry ness in a platinum cruci- 

 ble with a little nitric acid (sp. gr. 1-1 1-2), and the residue is 

 treated with ammonia and a few drops of a solution of strontium 

 acetate. If inosit is present, a greenish colouration is observed, 

 together with a violet precipitate. 



THE CANE-SUGAR GROUP. 



I. Saccharose. (Cane-sugar.) C 12 H 22 O a . 



Although it is not found as a constituent of any animal tissue, 

 this sugar possesses no inconsiderable interest in view of the fact 

 that it is a food-stuff which is largely consumed by man, and 

 may constitute in many cases no small part of the total carbo- 

 hydrates with which the body is supplied. 



Cane-sugar is chiefly distinguished from the others by the fact 

 that it does not reduce metallic salts, and does not form a com- 

 pound with phenyl-hydrazin ; but the property which is of great- 

 est interest to the physiologist is the ease with which it may 

 be 'inverted' or converted into equal parts of dextrose and 

 laevulose : 



C 12 H 22 O U -f H 2 = C 6 H 12 O 6 (dextrose) -f C 6 H 12 O 6 (kevulose). 



This inversion is readily brought about by treatment with dilute 

 mineral acids at 100, or even at 40 or below if the action is 

 more prolonged ; 2 it is also the result of the action of enzymes, 

 more especially of invertin from yeast, and is characterised ex- 

 perimentally by the change in the rotatory power of the solution, 

 which from being originally dextro-rotatory becomes Isevo-rotatory; 

 hence the name ' inversion.' For cane-sugar (a) D = -{-66 5 f r 

 Iffivulose (a) D = 100. The rotatory power of the latter is 

 largely dependent upon temperature and concentration. 



When cane-sugar is injected into the blood-vessels or tissues of 

 an animal it is eliminated in an unaltered condition, and is thus 

 shown to be non-assimilable. 3 On the other hand, it may be 

 introduced in large amounts into the alimentary canal without 

 reappearing externally in the urine. From this it may be con- 

 cluded that it undergoes some change before or during absorption, 

 and this change is most probably that of inversion. This change 

 may take place in the stomach, partly under the influence of the 

 acid of the gastric juice, but also as the result of the action of a 

 soluble enzyme ; 4 it is even more marked in the small intestine, 



1 Dissertation, Dorpat, 1884. Quoted by Fick. (Pharm. Zi. f. Russl.) See 

 Abst. in Ber. d. d. chem. Gesell. Jahrg. xx. (1887). Ref. Bd. S. 320. 



2 Cf. Wohl, Ibid. Jahrg. xxm. (1890), S. 2087. 



3 Bernard, Lecons de Phi/siol. exp. T. i. 1855, p. 219. 



4 Leube, Virchow's Arch. Bd. LXXXVIII. (1882), S. 222. Cf. Hoppe-Seyler, 



