NUTRITIVE VALUE OF FISH AND SHELLFISH 537 



LIVER OILS, laCHEST NATURAL SOURCE OF FAT-SOLUBLE VITAMINS 



In considering the dietary value of fish fats and oils one should 

 consider their value as a source of vitamins as well as of energy. 

 Considered from the stand])oint of vitamin content, the liver oils of 

 the family Gadidae (which includes cod, hake, haddock, and pollock) 

 are generally acknov/ledged to he the richest known source of the 

 antiophthalmic and antirachitic vitamins. The antiophthulmic 

 vitamin is also known as vitamin A, and the antirachitic vitamin is 

 sometimes referred to as vitamin D, 



It has been shown by the writer (Holmes, 1925) that the vitamin A 

 content of cod-liver oil is more than 100 tunes as potent as that of 

 dairy butter, which is believed to be one of the substances richest in 

 fat-soluble vitamins. The writer has also found that the liver oils 

 of pollock, hake, haddock, halibut, and dogfish have a high content 

 of vitamin A (Holmes, 1922 and 1924; Holmes and Pigott, 1925). 

 Other studies (Holmes, 1924a) show that the vitamin content of cod- 

 liver oil varies over wide limits, and that its extent is influenced to a 

 great degree by the condition of the fish from which the livers are 

 taken, as well as by manufacturing processes and storage conditions. 

 To prepare a wholesome, palatable cod-liver oil having a high vitamin 

 content it is necessary to use only strictly fresh livers, and these 

 should be cooked within a short time after the fish are caught. 



The process of manufacturing cod-liver oil is much like that of 

 making a cake. If the cook is provided with strictly fresh eggs she 

 should be able to prepare a tasty cake, at least in so far as the eggs 

 are concerned; but if stale, musty, or bad eggs are used it is difficult 

 if not impossible to make a satisfactory cake. In the same way if 

 cod livers have begun to decompose the oU obtained from them can 

 be used only for industrial purposes unless it is chemically processed. 

 By chemically treating industrial or even "rotted" cod-liver oil it is 

 possible to so improve the color, odor, and other characteristics that 

 such renovated oils will x>ass for medicinal cod-hver oil. In this 

 connection it is important to remember that such refining does not 

 increase the vitamin potency of these low-grade oils, which ordinarily 

 have little if any value as a source of vitamins. 



As noted above, large quantities of fish body fats that are inti- 

 mately associated with muscular tissues are eaten annually. The 

 question, therefore, naturally arises as to whether the fish body fats 

 also contain large amounts of the fat-soluble vitamins. Vitamin 

 tests were conducted by the author (Holmes, 1925a; Holmes and 

 Pigott, 1925a) to secure information conceiTiing the vitamin potency 

 of shad and salmon body fats, and it was found that these fats were 

 not as rich in vitamin A as were cod and other fish liver fats. 



Since in evaluating an edible fat one must consider both the energy 

 value and the vitamin content, it is of interest to note here the recent 

 work by Fridericia (1924) regarding the vitamin content of whale 

 fat. He reports that additions of 20 per cent hydrogenated whale 

 fat to the diet of experimental animals did not contribute sufficient 

 vitamin A to enable the animals to make scarcely any growth. 

 Furthermore, he shows that the hydrogenated whale fat actually 

 ha<l destructive action on the vitamin A content of butterfat when 

 the two fats were mixed after they had been melted. He very 

 properly points out the results that this undesirable property of 



