CH. XXVni.] THE CAEBOHYDRATES 413 



and ether. It is dextro-rotatory. With Trommer's test it gives a 

 blue solution, but no reduction occurs on boiling. 



With iodine it gives a reddish or port-wine colour, very similar to 

 that given by erythro-dextrin. Dextrin may be distinguished from 

 glycogen by (1) the fact that it gives a clear, not an opalescent, solu- 

 tion with water ; and (2) it is not precipitated by basic lead acetate 

 as glycogen is. It is, however, precipitated by basic lead acetate and 

 ammonia. (3) Glycogen is precipitated by 55 per cent, of alcohol ; 

 the dextrins require 85 per cent, or more. (4) It is precipitated 

 by saturation with ammonium sulphate; erythro-dextrin is only 

 partially precipitable by this means. 



Cellulose. This is the colourless material of which the cell-walls 

 and woody fibres of plants are composed. By treatment with strong 

 mineral acids it is, like starch, converted into glucose, but with much 

 greater difficulty. The various digestive enzymes have little or no 

 action on cellulose ; hence the necessity of boiling starch before it is 

 taken as food. Boiling bursts the cellulose envelopes of the starch 

 grains, and so allows the digestive juices to get at the starch proper. 

 Cellulose is found in a few animals, as in the outer investment of 

 the Tunicates. 



Inosite was discovered by Scherer in 1850 as a constituent of 

 muscle, and for a long time was known as muscle sugar. It occurs 

 also in small quantities in other animal organs (liver, kidney, etc.), 

 and in plants it is a fairly constant constituent of roots and leaves, 

 especially growing leaves. 



It has the same molecular formula as the simple sugars 

 (C 6 H 12 6 ), but it has none of the other properties of these substances. 

 Maquenne ascertained that it has the following formula 



HOH 



A 



HOH C C HOH 

 HOH C C HOH 



HOH 



which a mere glance at will show is very different from those of the 

 sugars given on p. 408. For the six carbon atoms, instead of forming 

 an open chain, are linked into a ring, as in the benzene derivatives. 

 It is in fact a reduced hexa-oxybenzene. It probably represents 

 a transition stage between the carbohydrates and the benzene 

 compounds. By a closing-up of the open chain of the carbo- 



