92 Microscopic Histochemistry 



mal and plant kingdoms. The classification which follows 

 does not claim completeness; it includes only such lipids as 

 are likely to be met with in normal and pathological tissues 

 of man and of the common laboratory animals. 



Classification of Lipids 



A. Paraffins (petrolatum). 



B. Isoprene derivatives (carotenoids). This gi-oup includes carotene, 

 vitamin A, visual purple, and some of the pigments of crustaceans. 



C. Fatty acids and their derivatives. 



a) Fatty acids. 



b) Soaps, especially those of Ca. Although soaps are insoluble in 

 fat solvents, they are included in this group for reasons of close 

 chemical relationship. 



c) Triglycerids (neutral fats). 



d) Waxes (long-chained alcohol esters of fatty acids). 



e) Phosphatids.2 



1. Lecithins (glycerine esterified with 2 molecules of fatty acid 

 and 1 molecule of phosphorylcholine ) . 



2. Cephalins (glycerine esterified with 2 molecules of fatty 

 acid and 1 molecule of either phosphorylcolamine or phos- 

 phorylserine ) . Lipositol is a complicated cephalin-like sub- 

 stance with inositol as an additional component. 



3. Plasmalogens (glycerophosphorylcolamine [or choline] in a 

 cyclic acetal linkage with 1 molecule of fatty aldehyde) . 



4. Sphingomyelin (sphingosine esterified with 1 molecule of 

 phosphorylcholine and in acylamide linkage with 1 molecule 

 of fatty acid). 



/) Cerebrosides.2 Sphingosine galactoside or glucoside in acylamide 

 linkage with 1 molecule of fatty acid (examples: kerasin, phren- 

 osin) are the simplest representatives of this group; there are 

 also more complicated ones containing several units of various 

 sugars and unidentified amino acid components. A special group 

 of cerebrosides contains sulfuric acid (see the review of Blix^ 

 on sulfur-containing lipids) . 



D. Lipid peroxides. 



E. Steroids. 



a) Cholesterol. 



2. Page, J. H.: Chemistry of the brain (Springfield, 111., and Baltimore, 

 Md.: C. C. Thomas, 1937). 



3. Blix, C: Ztschr. f. physiol. Chem., 219:82, 1933. 



