784 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



isomer of 2-hydroxypalmitic acid. Lanocerotic acid is a dihydroxy acid 

 with an empirical formula, C30H60O4, which has also been identified in wool 

 wax. 433 - 434 



The principal fatty acids in wool fat and hair fat are the iso- and anteiso- 

 acids listed as Groups 3 and 4- In Group 3, the iso-acids have the methyl 

 group in the penultimate position; the acids have an even number of car- 

 bons, although the fatty acid chains contain an odd number of carbons. 

 In Group 4, in which the methyl side chain is attached to the antepenulti- 

 mate carbon, the compounds have an odd number of carbon atoms, al- 

 though the fatty acid chain is an even one. 



Weitkamp, Smiljanic, and Rothman 435 have reported that the free fatty 

 acid fraction of human hair fat consists of normal saturated and unsatu- 

 rated acids ranging in chain length from 7 to 22 carbon atoms. The 6,7- 

 position was found to be the characteristic location of the double bond in the 

 unsaturated acids, although some A 8>9 -acids, as well as other isomers, were 

 found. The following proportions of acids in Group 3 were noted: C 8 , 

 0.15%; C10, 0.33%; C 12 , 3.5%; C 14 , 9.5%; C 16 , 36%; C 18 , 23%; C 20 , 

 8.5%; C 22 , 2.0%; and higher than C 22 , 4.0%. The anteiso-acids (Group 

 4) 435 were present as follows: C 7 , 0.07%; C 9 , 0.20%; C n , 0.15%; Ci 3 , 

 1.4%; C15, 6.0%; and Cn, 6.0%. For a further discussion of the nature 

 of these wool fatty acids, the reader is referred to Volume I, pages 36, 37, 

 and 370. 



(3) Lipids Present in the Sebum 



The sebum represents the secretion of the sebaceous glands of the skin. 

 In the fur-bearing animals, this secretion emerges at the roots of the hair. 

 In birds, the coccygeal or preen gland, located at the base of the tail, has a 

 function similar to that of the sebaceous gland ; it secretes lipids important 

 in the functioning of feathers. 



The nature of the secretion of the sebaceous glands varies with the posi- 

 tion in which the glands are located. Cerumen, the waxy secretion of the 

 outer ear, is a specialized type of sebum. The sebaceous glands located in 

 the feet, armpits, and anus secrete more neutral fat than do glands from 

 other parts of the skin ; the unpleasant odor from these areas (bromidrosis) 

 is believed to be due to the rancidity of this fat. In the disease known as 

 seborrhea, the secretion of the sebaceous glands is increased. 436 



The composition of sebum is ill-defined because of the difficulty of ob- 



436 A. W. Weitkamp, A. M. Smiljanic, and S. Rothman, /. Am. Chem. Soc, 69, 1936- 

 1939 (1947). 



436 M. R. Everett, Medical Biochemistry, 2nd ed., Hoeber, New York, 1946, p. 229. 



