124 HANDBOOK OF PHYSIOLOGY. 



concentrated solutions by absolute alcohol. It has no power of reducing 

 copper salts on boiling. It is dextro-rotatory (see Appendix). It is not 

 subject to alcoholic fermentation, until by inversion it is converted into 

 glucose, it chars on addition of sulphuric acid, and on heating with po- 

 tassium or sodium hydrate. 



Lactose is the chief carbohydrate of milk. It is less soluble in 

 water than glucose ; not sweet, and is gritty to the taste ; but it is insolu- 

 ble in absolute alcohol. In digestion it yields a molecule of dextrose and 

 a molecule of galactose. Undergoes alcoholic fermentation with extreme 

 difficulty ; gives the tests similar to glucose, but less readily. It is dex- 

 tro-rotatory -|- 59. 



Maltose is produced by the action of the saliva and pancreatic juice 

 on starch. It is also formed by the action of malt upon starch by the 

 ferment diastase, and in the formation of glucose from starch. It is con- 

 verted into dextrose by dilute sulphuric acid. It is dextro-rotatory; fer- 

 ments with yeast; reduces copper salts, and crystallizes in fine needles. 



Glucose occurs widely diffused in the vegetable kingdom, in diabetic 

 urine, in the blood, etc. ; it is usually obtained from grape-juice, honey, 

 beet-root or carrots. It really is a mixture of two isomeric bodies, Dex- 

 trose or grape-sugar, which turns a ray of polarized light to the right 

 (-J- 50), and Lccndose or fruit- sugar, which turns the ray to the left. 



It is easily soluble in water and in alcohol ; not so sweet as cane-su- 

 gar ; the relation of its sweetness to that of cane-sugar is as 3 to 5. It is 

 not so easily charred by strong sulphuric acid as cane-sugar. It is not en- 

 tirely soluble in alcohol. It undergoes alcoholic fermentation with yeast. 



Dextrose is the characteristic carbohydrate of the blood. It has the 

 power of reducing the salts of silver, bismuth, mercury, and copper, either 

 to the form of the metal in the first three cases, or to the form of the 

 siiboxide in the case with cuprous salts. Upon this property the chief 

 tests for the sugar, e.y., Trommer's and Bottcher's, depend (see Appen- 

 dix). When boiled Avith potash, glucic and melanic acids are formed, 

 and a yellowish fluid results (Moore's test). It is oxidized by the action 

 of nitric acid to saccharic acid. It forms compounds with acids and with 

 potash and lime. It undergoes alcoholic fermentation with yeast, and 

 lactic-acid fermentation with bacteria lactis. It forms caramel when 

 strongly heated, and is also charred with strong acids. For the method 

 of quantitative estimation, etc., see Appendix. 



Laevulose is one of the products of the decomposition of cane-sugar 

 by means of dilute mineral acids, or by means of the ferment invtrtin in 

 the alimentary canal. 



It reacts to the same test as glucose, but is non-crystallizable, and is 

 laevo-rotatoiy-1060. It is soluble in water and in alcohol. Its com- 

 pound with lime is solid, whereas that with dextrose is not. 



