CONSTANTS FOR IDENTIFICATION OF FATS AND OILS 237 



hexaenoic acids, especially in the phosphatides, after the administration of 

 cod-liver oil. 



Although butyric, caproic,'^^-^^^ and caprylic^^^ acids cannot be deposited 

 by the rat in storage fat, even when the triglycerides of these acids are fed 

 in large quantities, capric and lauric acids, ^^^-^'^ as well as myristic acid,^^^ 

 are capable of being deposited in the storage fat when their triglycerides 

 comprise an important part of the diet. It has recently been demon- 

 strated in a most convincing manner that the triglyceride of an odd-chain 

 acid, triundecylin, can be laid down in rat tissues when the unnatural fat is 

 fed over a protracted period. *^^ As much as 24% of the undecylic acid was 

 found in the storage fats after a 6- week feeding period during which triun- 

 decylin was given. 



A hard body fat with low iodine number results when a high carbohydrate 

 or high protein diet is given. Anderson and MendeP^^ reported that, when 

 cornstarch was substituted equicalorically for fat in the diet of rats, a pro- 

 gressive hardening of the body fat ensued. Great commercial importance 

 may sometimes be attached to such variations in the type of fat produced. 

 After hogs partook of a large proportion of peanuts, a "soft pork," in which 

 the fat was partially licjuid, resulted, giving a product unacceptable to the 

 consumer.^i^'^*-" According to EUis and Isbell,^"^^ fats having a high iodine 

 number and a low melting point are produced in hogs when either peanuts 

 or soybeans make up a large proportion of the diet; on the other hand, the 

 ingestion of corn and skimmed milk or brewer's rice and tankage produces 

 fats with a low iodine value and a relatively hard consistency. These 

 examples of variations in the composition of natural fats emphasize the fact 

 that wide ranges in the constants are perfectly normal. 



(1) Melting Point 



In some cases the nature of a fat may be determined from its melting 

 point. This value is of little use in the case of the vegetable oils, since 

 these are mostly liquid at ordinary' temperatures. The same fat may ex- 

 hibit several different melting points, depending upon the polymorphic state 

 in which it exists — see discussion of poh^morphism, Section 6(1). Be- 



»'« H. C. Eckstein, J. Biol. Chem., 81, 613-628 (1929). 



»» H. C. Eckstein, J. Biol. Chem., 84, 353-357 (1929). 



3»* M. Powell, J. Biol. Chem., 89, 547-552 (1930). 



»'6 M. Powell, J. Biol. Chem., 95, 43-45 (1932). 



3" F. E. Vis.scher, /. Biol. Chem., 162, 129-132 (1940). 



"8 W. E. Anderson and L. B. Mendel, J. Biol. Chem., 76, 729-747 (1928). 



"9 O. G. Hankins and X. R. Ellis, V. S. Dept. Agric, Dept. Bull. Xo. 1407 (April, 

 1926). 



32" (). C;. llankins, X. R. Elli.s, and .J. H. Zeller, U. S. Dept. Agric, Dept. Bull. Xo. 1492 

 (Feb., 1928). 



"' X. R. Ellis and H. S. Ishell, J. Biol. Chem., 69, 239-248 (1926). 



