THE MUTUAL RELATIONS. 303 



The relations to the fats are evident from the following formulae: 



CH 2 OH COH COOH 



I I I 



CHOH CHOH CHOH 



CH 2 OH CH 2 OH CH 2 OH 



Glycerol Glycerose Glyceric acid. 



(Glyceraldehyde) 



Glycerose is simply the aldehyde of glycerol. 1 Its preparation from 

 glycerol was accomplished by Emil Fischer. Conversely, we can imagine 

 one of the fat components, glycerol, as originating from glycerose. The 

 relations become much more complicated if we attempt to derive the 

 fatty acids, the other components of fats, from sugar. Emil Fischer 2 

 suggests their formation in the following manner: To produce oleic and 

 stearic acids, three molecules of grape-sugar (or six molecules of glycerose) 

 may unite at their aldehyde groups, thus forming a chain of 3 X 6 = 18 

 carbon atoms. By rearrangement of the atoms and withdrawal of oxygen, 

 i.e., by reduction, the above-mentioned acids may be formed. The other 

 fatty acids, e.g., palmitic acid, can be formed perhaps in a similar manner, 

 except that sometimes only hexoses are used for the synthesis, while, at 

 other times, hexoses and pentoses are both utilized, according to the 

 number of carbon atoms in the acid molecule. Thus we can imagine 

 palmitic acid, with its 16 carbon atoms, being produced from one 

 hexose and two pentose molecules. Pentoses are very widely distributed 

 in the vegetable world, and in large amounts. They play a far less 

 important part in the animal body, although they may be formed by 

 decomposition. We have already learned that a pentose, arabinose, may 

 be very easily derived from glucose, or from gluconic acid; and on the 

 other hand, we have seen that an oxidation product of glucose, glucuronic 

 acid, will easily go over into a five-carbon sugar by splitting off carbon- 

 dioxide. 



Thus, while we are in a position to derive one of the components of the 

 fats, glycerol, from the carbohydrate group, we have but little foundation 

 for the formation of fatty acids from the same group. We are at present 

 confined to hypotheses. We have not yet succeeded by any chemical 

 means in converting sugars into fat. 



1 The original glycerose, with which Fischer worked, really contained chiefly 

 dihydroxyacetone. von Lippmann and others, however, prefer to call glyceral- 

 dehyde (of which there are two stereo isomers) glycerose rather than the dihydroxy- 

 acetone. TRANSLATORS. 



2 Die Chemie der Kohlehydrate und ihre Bedeutung fur die Physiologic, Berlin, 

 A. Hirschwald, 1894, p. 28. 



