CHAPTER XX 

 THE LIPOIDS OF MICRO-ORGANISMS 



THE term " lipoid " (lipide and lipin are sjTionymoiis) 

 is employed as a general name for all the fat-like 

 substances which are soluble in the " fat solvents " 

 ether, alcohol, acetone, chloroform and light petroleum. 

 Thus the f?«ts, waxes, higher alcohols, sterols and phos- 

 phatides, together with certain of their degradation 

 products, such as fatty acids and glycerol, are all lipoids. 

 Fats. — The fats are all glycerides, that is, esters of 

 fatty acids with glycerol. When it is remembered that 

 glycerol, CH2OH.CHOH.CH2OH, contains three hydroxyl 

 groups capable of esterification and one, two or three 

 of them may be involved, that the acids attached may 

 be all the same or all different and may be chosen from 

 a large number, both saturated and imsaturated, it is 

 obvious that a great variety of fats is possible. Usually 

 fats occur together as complex mixtures which are 

 extremely difficult to separate, and their analysis is 

 restricted to the identification of the fatty acids present 

 and the determination of the ratio of saturated to un- 

 saturated fatty acids. The fats of micro-organisms 

 usually contain a high proportion of unsaturated fatty 

 acids and are consequently liquid at ordinary temperatures 

 or have low melting points. Palmitic, C16H32O2, stearic, 

 CigHgeOg, and oleic acids, C18H34O2, are the chief acids 

 found in the fats of micro-organisms as they are in animal 

 fats, but butyric, C4H8O2, caproic, C6H12O2, lauric, 

 C12H24O2, dihydroxystearic, C18H36O4, linoleic, CigHggOa, 

 linolenic, C18H30O2, tuberculostearic, C19H38O2, arachidic, 



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