164 VITAMIN D GROUP 



of young carnivora in captivity to ensure their successful development . . . 

 Further, it is commonly known that if herbivora, e.g., horses, are scrubbed 

 thoroughly with soap and w^ater, they do not thrive. It may thus be inferred 

 that the sebaceous secretion of the preen gland of birds ... is an important 

 source of vitamin D in the mammal." 



Hou^®^ found that rickety chickens with preen glands removed could be 

 cured by irradiating the feet, even though irradiation of the body or of the 

 head was ineffective. In this case the substance activated was obviously 

 neither preen gland oil nor circulating blood, but something in the tissues 

 of the feet which was directly absorbed. 



Evidence enough has been presented to show that the higher animals ob- 

 tain vitamin D in at least three ways, the relative importance of which 

 must vary with the habits, requirements, and opportunities: (1) by eating 

 such foods as eggs, fish, whole furred or feathered animals, and insolated 

 dead vegetable tissues; (2) by ingesting insolated sebaceous matter in the 

 process of neatening the body — licking and preening; and (3) by directly 

 absorbing the products of insolation formed on or in the skin. 



The occurrence of vitamin D in fishes is a phenomenon of great biochemi- 

 cal, as well as practical, interest. Nearly all fish oils contain vitamin D, 

 but the amount varies prodigiously with the species (Table III) and other 

 factors. Both free and esterified forms are present. ^°' ^^^ 



The principal fat storage depots of fish are the muscle tissue and the 

 liver. Some fat is also found in the viscera and head. Species which store 

 much oil in the muscle, such as salmon, have small livers which contain 

 little oil. Species which store little oil in the muscle, such as cod, have large 

 livers which contain much oil. The amount of oil w^hich is stored in muscle 

 or liver depends on the abundance of food and the demands of spawning 



The occurrence of vitamin D in fish body oils was first noted by Bills^^" 

 in experiments with commercial menhaden oil. In most physicochemical 

 characteristics the liver and body oils of a given species are similar, but the 

 concentration of vitamin D is generally higher in the liver oil. In some 

 species, such as the tunas, the liver oil may contain several thousand times 



166 H. C. Hou, Chinese J. Physiol. 5, 11 (1931). 



'67 C. E. Bills, F. G. McDonald, O. N. Massengale, M. Imboden, H. Hall, W. D. Her- 

 gert, and J. C. Wallenmeyer, /. Biol. Chem. 109, Proc. vii (1935). 



168 D. S. Jordan, B. W. Evermann, and H. W. Clark, Check List of the Fishes and 

 Fishlike Vertebrates of North and Middle America North of the Northern Bound- 

 ary of Venezuela and Columbia. Report of the U. S. Commissioner of Fisheries 

 for the Fiscal Year 1928 with Appendixes, Part 2. Gov't Printing Office, Washing- 

 ton, 1930. 



169 K. C. D. Hickman, Ind. Eng. Chem. 29, 1107 (1937); K. C. D. Hickman and E. L. 

 Gray, ihid. 30, 796 (1938). 



"" C. E. Bills, Studies on the Antiricketic Vitamin: Dissertation. Johns Hopkins 

 Press, Baltimore, 1924. 



