Formation of Fatty Acids 



261 



Beeckmans, 1950). The data of Table I show that the short- 

 chain acids could not have originated from the degradation 

 of oleic acid as postulated by Hilditch, but must have been 

 synthesized from acetate. 



Table I 



"C Content (1 x 10-^ /xc./mg. C) of Glyceride Fatty Acids in Mammary 

 Glands of Non-lactating 28 Days-pregnant Rabbits Injected Intra- 

 venously with CHg^^COONa 



Volatile fattv acids: — 

 Water-soluble (Ci-Cg) 

 Water-insoluble (Cg-Cij) 



Non-volatile fattv acids: — 

 Solid . . . . . 

 Liquid 



Exp. 1* 



Exp, 2* 



*In Exp. 1 two equal injections of the labelled acetate were given daily for 4 days; the total 

 **C dose was 50/uc. (4-3 nig. of acetate). In Exp. 2, two injections, 50 ^c. each, were given 

 6 hours apart and the animal was killed 20 hours after the first injection. 



In these experiments on pregnant rabbits, the fat extracted 

 from the mammae contained volatile acids and in this respect 

 was comparable to milk fat, but the extent of its admixture 

 with tissue fat could not be ascertained. In order to continue 

 these observations it was desirable to obtain adequate quan- 

 tities of true milk fat for detailed study over a period which 

 also allowed the time course of the synthetic process to be 

 followed. For this purpose a lactating goat of 117 lb. body 

 weight was injected intravenously with 5 mc. of CHg^^COONa 

 (430 mg.) and was then milked at frequent intervals up to 

 48 hours after the injection (Popjak, French and Folley, 

 1950, 1951). It is of particular interest to mention here (the 

 goat being a ruminant) that it has b.een shown by Barcroft 

 and his collaborators that ruminants assimilate their carbo- 

 hydrate food as acetic acid, by fermentation of cellulose and 

 other polysaccharides in the rumen (see review by Elsden 

 and Phillipson, 1948). Thus acetate is of particular impor- 

 tance in ruminant metabolism. 



