CHAPTER IX. 

 LIPOIDS. 



" LIPOIDS " is the collective name for fatty substances. 1 Many of 

 them are not moistened by water; however, this property is not 

 characteristic of all lipoids. 



Fats and oils are esters of higher fatty acids, usually with glycerin, 

 which may be substituted by other higher alcohols; for instance, a 

 palmitic acid ester of cetyl alcohol occurs in spermaceti, found in the 

 skull of the sperm-whale. Though in other fats all three hydroxyls 

 of glycerin are replaced by fatty acid radicals, in the lecithins only 

 two fatty acid radicals occur, and the third hydroxyl group is re- 

 placed by a phosphoric acid-cholin radical. Cholin is a trimethyl- 

 oxyethylammoniumhydroxid. 



Formula of Fats. Formula of Lecithin. 



CH 2 O-fatty acid CH 2 O-cholin-phosphate 



CHO-fatty acid CHO-fatty acid 



CH 2 O-fatty acid CH 2 O-fatty acid 



Finally, we must consider cholesterins and isocholesterins, which we 

 may regard as complex terpenes. 



The characteristic fats, the triglycerides, are universally distributed 

 in the animal body, where they play an important part in maintaining 

 the body heat, while in plants they are of much less importance. 

 Lecithins are found distributed throughout the animal organism, not 

 only in the chief depots, the brain, nervous tissue generally and the 

 egg yolk, but in every cell, every organ, even in the lymph, blood 

 corpuscles and muscles. In plants too, lecithin is widely distributed, 

 occurring in the seeds. 



The fact that lecithins occur in all parts of the body is an evidence 

 of their great biological importance. So far as may be gathered 

 from previous researches, they play an important role in the life- 



1 Various investigators give different definitions of the term " lipoids." BANG 

 uses it most inclusively and regards everything in the body soluble in organic 

 solvents as lipoid; S. LOEWE gives it the narrowest scope, and includes only sub- 

 stances which form colloid solutions in organic solvents (e.g., cephalin, cerebrosid). 



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