678 VII. VITAMINS A 



sence as shown by tests of 150 g. of oil obtained from the bodies of a large 

 number of cockroaches. There has been a conviction in some quai'ters that 

 the invertebrates lack vitamin A. This theory has been supported by the 

 failure to identify vitamin A in any tissue. Moreover, large hauls of zoo- 

 plankton, consisting principally of invertebrate material, failed in a number 

 of instances to show even traces of vitamin A.™'^ However, it has now 

 been proven that high concentrations of vitamin A are present in the ret- 

 inas not only of the vertebrates but also of the invertebrates. In the 

 earlier studies on invertebrates, the presence of vitamin A had been over- 

 looked because the retinas constituted such a relatively insignificant pro- 

 portion of the total body tissues. 



(5) Distribution of Vitamins Ai and Ao 



Although the usual form of vitamin A (vitamin Ai) is the predominant 

 type in which this compound occurs naturally, a second form, vitamin A2, 

 has been found in the livers of fresh-water fishes. The presence of this 

 additional kind of vitamin A was fiist suspected as a result of variations in 

 the reaction of certain fish liver oils to antimony trichloride. This phenom- 

 enon was first observed by Heilbron, Gillam, and Morton^^ as early as 

 1931. These workers found that absorption bands appeared at 690-700 

 mn and 635 to 655 m/x when some fish liver oils w^ere treated with antimony 

 trichloride, as well as in the usual area of 615-620 myu. They postulated 

 that one or more chromogenic substances, in addition to vitamin A, were 

 present, but they did not realize that another form of vitamin A was re- 

 sponsible for the anomalous reaction. 



Edisbury, Morton, and Simpkins^^ found that an absorption band only 

 rarely developed at 693 m/i when cod liver oil was treated with the Carr- 

 Price reagent, and never occurred when whale oil was similarly treated, but 

 that a marked positive response usually obtained in the case of halibut 

 liver oils, as well as of the visceral oils of this species. The ratios of ab- 

 sorption at 693 : 620 mju were usually approximately 1 : 6 in the case of the 

 hepatic fat, and 1 : 10 in the body fat of the halibut. However, in the eyes 

 of the goldfish (Carassius auratus), the intensity of the 693 m^u band was 1.5 

 greater than that at 620 m/x.^^ In the brown trout, only the 693 m^u band 

 could be detected. This led Edisbury, Morton, and Simpkins'^^ to suggest 

 that the chromogen responsible for the 693 mju band should be regarded as 

 vitamin A2, because its distribution suggested that it could replace vitamin 

 Ai in the fresh-water fish. Almost simultaneously, Lederer and Rosan- 



'0 J. C. Drummond and E. R. Guiitlu-r, J. Exptl. Biol., 11, 203-209 (1934). 

 " A. E. Gillam, M. 8. El Ridi, and R. S. Wimpennv, /. Exptl. Biol, 16, 71-88 (1939). 

 '2 I. M. Heilbron, A. E. Gillam, and R. A. Morton, Biochem. J., 25, 1352-1366 (1931). 

 " J. R. Edisbury, R. A. Morton, and G. W. Simpkins, Nature, I40, 234 (1937). 



