CHAPTER XXVIII 



FATTY SUBSTANCES * 



648. Nomenclature. 



Each of the general terms in use has more than one meaning. 

 The following outline of current usage is based chiefly on Sperry's 

 discussion of nomenclature {A Textbook of Biochemistry, ed. 

 B. Harrow and C. P. Sherwin. Saunders, Philadelphia and 

 London, 1935, p. 109). 



Each of the words, fat, lipoid, lipide, lipid, lipin, may denote 

 either (1) fatty substances in general or (2) one or more groups 

 of fatty substances defined according to chemical properties. Fat 

 in the restricted sense denotes glyceryl esters of fatty acids, com- 

 pounds referred to also as neutral fats or true fats. Lipoid in the 

 restricted sense may denote either (1) fatt^ substances exclusive of 

 neutral fats or (2) fatty substances containing nitrogen. Used with 

 reference to the results of histological examination of tissue 

 sections lipoid usually denotes sudanophil substances either shown 

 or assumed to contain cholesterol. Biochemists are agreed that 

 the word lipoid should be abandoned in favour of lipide, lipid, or 

 lipiri, but the relative claims of these words are unsettled and no 

 definition of any of them is universally accepted. 



The only general terms used in this chapter are ^^ fat " and '''^ fatty 

 substances " ; each of these terms covers fatty acids and soaps, 

 glyceryl esters of fatty acids, waves, sterols and their esters, phos- 

 phatides and cerebrosides. 



649. Scope of Histological Methods. The fat that can be 

 studied by histological methods forms a variable fraction of the 

 total fat content of any tissue. This fraction may be termed 

 visible to distinguish it from the invisible fraction whose existence 

 can be established only by chemical analysis. 



Many methods have been devised for the study of visible fat, but 

 common experience and critical examination have shown that few are 

 really valuable. The outlook on fat staining has been revolu- 

 tionised during the past ten years. Of the many studies that have 

 contributed to this change, those of Kaufmann and Lehmann 

 (1926 a and h, 1928-29, 1929, 1932) and Lison (1933 a and b, 1934, 

 1935 a and b, Lison and Dagnelie, 1935) deserve special mention. 

 Lison's work is summarized in his recent book (1936). His first 

 paper (1933 a) is a critical review covering almost the whole of the 

 literature. The reader is referred to the following literature : 



* By W. W. K. and R. W. 



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