192 III, CHEMISTRY OF NEUTRAL FATS 



fat. Hexadecenoic acid made up 7%, oleic acid 38%, and linoleic acid^^° 

 22%. A surprising uniformity in the composition of abdominal, gizzard, 

 and neck fats was noted both in young and in old birds. In the case of sea 

 birds, a considerable increase in the proportion of C20-C22 unsaturated 

 acids obtains, with a corresponding decrease of the Cis unsaturated acids 

 and palmitic acid. Thus, the fat of these birds resembles that of the 

 aquatic animals more than that of the land species. Lovern^^^ has sug- 

 gested that this atypical composition may result from the diet of sea food; 

 furthermore, sea birds may have no specific requirements, and any type of 

 depot fats may serve equally well. 



The fat of rats and pigs has been the subject of many investigations. 

 Where the proportion of fat in the diets is sufficiently low, so as not to 

 influence the type of fat laid do\vn, the fat from the rat and pig is com- 

 posed of 25 to 30% of palmitic acid and only 5 to 10% of stearic acid. The 

 unsaturated acid is chiefly oleic, which may comprise 45 to 50% of the 

 total; considerable amounts of palmitoleic acid also occur, with only 

 traces of the higher acids. When the composition of the fat is altered by 

 diet, no change takes place in the proportion of stearic acid, but a marked 

 decrease in both palmitic and palmitoleic acids obtains. The new food fat 

 may replace the fatty acids which have disappeared. Such fatty acids as 

 lauric, myristic, linoleic, linolenic, and arachidonic can all be more or less 

 effectively added to the body fat. Beadle et al.,^^"^ in fact, have recently 

 proved that as much as 27.6% of the fatty acids present in rats, and 

 11.4% of that composing pig fat, may consist of trienoic acids (chiefly 

 linolenic) if a large proportion of this type of unsaturated acid is fed. 



Less information is available as to the fat composition in the higher spe- 

 cies. In the case of beef and mutton tallow, only three fatty acids are pres- 

 ent in any appreciable amounts, namely, palmitic, stearic, and oleic acid. 

 These are present to the approximate extent of 25-30%, 20-25%, and 40- 

 45%, respectively. ^^^ The composition of the fat of steers is much less in- 

 fluenced by the feeding of unsaturated acids than is that of the rat and 

 pjg 194 Although arachidic acid is normally nob present in the fat of the 

 pig, definite amounts are found after the animals have received large 

 amounts of peanuts over a period of time.^^^ 



It was recognized at an early date that human fat contains palmitic, 



190 T. p. Hilditch, E. C. Jones, and A. J. Rhead, Biochem. J., 28, 786-795 (1934). 

 I" J. A. Lovern, Biochem. J., 32, 2142-2144 (1938). 



192 B. W. Beadle, O. H. M. Wilder, and H. R. Kraybill, J. Biol. Chem., 175, 221-229 

 (1948). 



193 A. Banks and T. P. Hilditch, /. Soc. Chem. hid., 51, 111-114T (1932). 



19^ B. H. Thomas, C. C. C'ulbertson, and F. Beard, Proc. Am. Soc. Animal Production, 

 27 193—199 (1934) 



195 N. R. Ellis and H. S. Isbell, ./. Biol. Chem., 69, 219-238 (1926). 



