CHAPTER I 

 INTRODUCTION 



The chemical nature of most of the components of the lipids has become 

 fairly well understood within recent years. Methods of synthesis have been 

 developed for many of the substances, and precise data on many of the 

 physical constants have been obtained. 



At the present time, it is fairly safe to say that the fatty acids are the 

 best known group of the lipids. Although the chemical information con- 

 cerning most of these acids is quite complete, the biochemical data are 

 fragmentary. This is especially the case with the unsaturated acids. 

 For example, although oleic acid was described as early as 1815 by Chevreul, 

 and its structure has been understood since 1894 when Baruch 1 established 

 the position of the double bond, little is definitely known of its degradation 

 products and of the compounds involved in its in vivo synthesis. Informa- 

 tion as to the precursors and decomposition products of the doubly un- 

 saturated acids is even more limited than is knowledge concerning oleic 

 acid. 



The neutral fats comprise the type of lipids most widely distributed in 

 animal and plant tissues. The physical and chemical properties of various 

 simple mixed triglycerides have been carefully recorded; considerable 

 data are likewise available on the different mono- and diglycerides. A 

 wide variety of methods for the synthesis of these products has been 

 published. However, little is known of the biochemical factors which 

 control the type of triglycerides which are synthesized in the tissues. Our 

 knowledge of the mechanism of formation of the neutral fats from carbo- 

 hydrate and from protein is largely hypothetical. 



Biochemical information concerning the other classes of lipids is likewise 

 much less complete than are the strictly chemical data regarding them. 

 Probably most is known about the biochemical changes of lecithin and 

 related products, since such reactions are closely tied in with metabolic 

 changes of neutral fats and fatty acids. Cholesterol is still an enigma, 



1 J. Baruch, Ber., 27, 172-176 (1894). 



