THE ORGANIC ELEMENTS. 21 



gum is dextrin. Some time ago I advanced the opinion that dextrin 

 must be present in plants where so much cellulose and starch was dis- 

 solved and changed. Soon after, Mitscherlich pointed out the actual 

 presence of this substance in the sap of many plants. The principal 

 difference between gum and dextrin consists in the fact, that the latter, 

 by the action of dilute sulphuric acid or diastase, is converted into 

 grape-sugar, while the first is not. Gum apparently originates in the 

 plant from dextrin, and not as a special product of secretion ; whilst 

 dextrin is present in all the juices of the plant, and especially where 

 cells are about to be formed, and appears to be the formative matter of 

 the plant. Countless almost, however, are the modifications of dextrin, 

 through vegetable jelly, till it forms cellulose. 



6. Sugar. In a solid state, and entirely pure, sugar is crystalline, 

 clear, and easily soluble in water. In some states it is unerystallisable, 

 and then, through foreign substances, coloured yellow or brown. It is 

 slightly soluble in alcohol, but not in ether, volatile and fixed oils. It 

 mixes with a solution of iodine. The analyses give, according to various 

 modifications, various results : 



Anhydrous salt of sugar, with oxide of lead, 1 C H O 

 according to Berzelius and Liebig - - J 12 10 10 



Crystallised cane sugar, according to Gay- \io 11 11 

 Lussac, Thenard, Berzelius, and Liebig - J 



Grape sugar, from a crystallised compound 1 C H O 

 with common salt, according to Brunner - J 12 12 12 



The same from grapes, honey, and starch, ac- \ , 14 14 

 cording to Saussure and Prout - J 



Sugar, which is principally distinguished by its sweet taste, is by 

 various modifications, and in every case through inulin, connected with 

 the other bodies, birt of the transitionary conditions we know but little. 

 It presents itself very widely In the vegetable kingdom, and especially 

 where starch and the other substances are developing or are dissolved, 

 as in unripe peas and cereal grains ; and the early sap of trees, as of the 

 maple and beech. It is found in greater quantities, and in a more per- 

 manent form, in the stems of grasses, as the sugar-cane and maize, and 

 the Holcus saccharatus; in fleshy roots, as in the carrot and beet; and in 

 juicy fruits, as the pear and apple, gooseberry and currant. Naturally 

 it is found dissolved in the plant, but when it becomes excreted it assumes 

 the forms of crystals, as in the nectaries of plants (ex. gr. Fritillaria 

 imperialis). Mannite, the sugar of manna, does not belong to this series 

 of compounds. It is only the product of the decomposition of the sugar 

 cane. Its formula is C6 H7 O6. According to Mitscherlich, the 

 Tamarix gallica, which yields manna, contains in its tissues no mannite, 

 but cane sugar. 



7. Inulin (Dahlin, Calendulin, Synantherin, Sinistrin). It is obtained 

 from the tubes of the dahlia by simply washing. It is a powder with 

 fine grains ; the grains clear, easily soluble in boiling water, from which 

 it separates, on cooling, in a granular form. It is insoluble in ether and 

 alcohol, coloured yellow by iodine. Cold water makes the grains to dis- 

 appear to the eye under the microscope, because their refracting power 

 is similar to that of water. Hence the erroneous assertion of Link and 

 Meyen, that inulin is always in solution in plants. Crookewitt found 

 that inulin, by being boiled in water fifteen hours, was converted into an 



