38 PHYSIOLOGICAL CHEMISTRY 



Combination of Carbohydrates With One Another, and With 

 Other Substances. The carbohydrates have the property of 

 combining with various substances including themselves. The 

 union of two molecules of monosaccharide forms the disac- 

 charides, of many molecules of monosaccharide, the polysac- 

 charides. Compounds of monosaccharides with other classes of 

 materials are variously named, and include substances of great 

 biological interest and importance. Examples are the glucosides, 

 compounds of glucose or one of its derivatives, among which 

 are many of the drugs used in medicine, and some of the constit- 

 uents of brain and nerve tissue. The term "Glucosides" is 

 sometimes extended to include similar compounds which yield 

 other sugars, e.g., galactose. 



Behavior With Strong Alkalies. The action of weak alkali 

 upon the carbohydrates already has been discussed under the 

 heading interconversion of carbohydrates. A rearrangement of 

 groups in the molecule is observed. The action of strong alkali 

 is much more vigorous and far reaching and the nature of the 

 products formed depends upon the experimental conditions. 

 The alkali undoubtedly combines with the sugar at first. There 

 follows loss of water from groups around neighboring carbon 

 atoms, and a double bond is formed. The carbon chain is then 

 broken, and two compounds are formed, each with a smaller 

 number of carbon atoms than the original substance. The nature 

 of these fragments is only imperfectly understood, but it may 

 be inferred from the final products of the reaction. In case oxy- 

 gen is supplied plentifully, the fragments are oxidized to the 

 corresponding acids. Of these a long list may be obtained vary- 

 ing in complexity from formic H . CO OH and oxalic acids 



CO OH to acids having 



COOH 



chains as long or only slightly shorter than the chain in the 

 original substance. Evidently the breaking up into fragments 

 may take place at various points in the chain, giving compounds 



