THE CHEMISTRY OF THE ANIMAL BODY. 1003 



CARBOHYDRATES. 



The important sugar of the blood and the tissues is dextrose. It is 

 derived from the hydration of starchy foods, and from proteid metabolism. 

 From dextrose the lactic glands manufacture another carbohydrate, milk- 

 sugar. Cane-sugar forms an article highly prized as a food. The study of 

 the various sugars or carbohydrates is of especial interest because their chemi- 

 cal nature is now well known. 



Carbohydrates were formerly defined as bodies which, like the sugars and 

 substances of allied constitution, contain carbon, hydrogen, and oxygen, the 

 carbon atoms being present to the number of six or multiples thereof, the 

 hydrogen and oxygen being present in a proportion to form water. Glycoses 

 include the monosaccharides like dextrose, CgH^Ogj disaccharides include, 

 for example, cane-sugar, C^H^On, which breaks up into dextrose and levu- 

 lose, while polysaccharides comprise such bodies as starch and dextrins, which 

 have the formula (C 6 H 10 O 5 ) n . 



In recent years the term glycose has been extended to cover bodies having 

 three to nine carbon atoms and possessing either the constitution of an 

 aldehyde-alcohol, CH(OH)CHO, called aldoses, or of a ketone-alcohol, 

 COCH 2 OH, called ketoses. These bodies also have hydrogen and oxygen 

 present in a proportion to form water, and the number of carbon atoms always 

 equals in number those of oxygen. According to their number of carbon 

 atoms they are termed trioses, tetroses, pentoses, hexoses, heptoses, octoses, and 

 nonoses. 



It has been shown (foot-note, p. 989) how from the asymmetric carbon atom in lactic 

 acid two configurations are derived. If a body (such as trioxybutyric acid) contains two 

 asymmetric carbon atoms, four configurations are possible, 



CH 2 OH CH 2 OH CH 2 OH CH 2 OH 



HCOH OHCH OHCH HCOH 



HCOH OHCH HCOH OHCH 



COOH COOH COOH COOH 



Similarly among the glycose-aldoses, a triose has two modifications ; a tetrose, four ; a pen- 

 tose, eight : a hexose, sixteen, etc. Thus in the following formula by the variations of H 

 and OH on the four asymmetric carbon atoms, sixteen possible hexoses may be obtained. 



CH 2 OH 



-C- 

 C 



-c- 



CHO 



The carbohydrates have well-defined optical properties, rotating polarized light to the 

 right or left, and are therefore designated as d- (dextro-) and I- (laevo-) respectively. An 

 inactive (i-) form consists in an equal mixture of the two others. Where the OH group 

 is attached on the right it may be indicated by the sign +, on the left by , or the + OH 

 may be written below, the OH above. 

 CHO CHO 



HCOH H H OH H 



Tnnw or CH 2 OH C C C C CHO 



HCOH 8t OH OH H OH 



CH 2 OH CH 2 OH 



d-Glucose. 



