318 PHYSIOLOGY AT THE FARM. 



juice of many ripening fruits. Thus there is no variety of 

 sugar to which the name fruit-sugar is properly applicable, 

 and the name " fructose " may be dispensed with. 



Substances allied to Sugar. There are several soluble sub- 

 stances allied to sugar, of which mannite and glycyrrhizine 

 merit a short notice. 



Mannite. Mannite differs from sugar in chemical constitu- 

 tion by the presence of more hydrogen than is sufficient to 

 convert the whole of its oxygen into water. It forms the 

 largest proportion of the laxative medicine known as manna. 

 This drug is the inspissated juice exuded from the true moun- 

 tain ash (Fraxinus ornus) which grows abundantly in Calabria 

 and Sicily. When the drug manna is digested in hot alcohol, 

 mannite is deposited in tufts of silky quadrangular prisms as 

 the solution cools. By heat mannite fuses into a colourless 

 liquid, which on cooling solidifies into a mass of radiated crystals. 

 Mannite is very soluble in water ; it has an agreeable taste. 



Besides being contained in manna, mannite has also been 

 found in considerable quantity in celery, onions, asparagus 

 shoots, and in certain kinds of fungi. It is also contained in 

 some descriptions of seaweeds, as in the Laminaria saccharina, 

 the saccharine tangle, a white exudation from which is eaten 

 by the inhabitants of Iceland. This tangle, when dried, is said 

 to contain as much as 12 or 13 per cent of mannite. Mannite 

 is also a constituent of the juice which exudes from many 

 varieties of apple and pear trees, and it is formed in what is 

 termed the viscous fermentation of sugar, to which the beet- 

 sugar is particularly liable. 



Glycyrrhizine. Glycyrrhizine is the essential principle of 

 liquorice, or the extract of the root of the Glycyrrliiza gldbra. 

 The Italian liquorice is obtained from the Glycyrrhiza echin- 

 ata. Glycyrrhizine is not susceptible of fermentation. When 

 boiled for some hours with hydrochloric acid, it separates into 



