CHAPTER VII 



DISTRIBUTION, PROPERTIES, AND 

 CHEMISTRY OF THE VITAMINS A 



1. Introduction and Historical Development 



Although cod liver oil has for many years enjoyed a high reputation as a 

 therapeutic product, the causative agent which is responsible for its efficacy 

 was not recognized until well into the twentieth century. The discovery 

 of the cause for its beneficial activity was complicated by the dual nature of 

 the curative factors in this oil: (1) the factor which controls the antixer- 

 ophthalmic behavior of vitamin A; and (B) the factor which exhibits the 

 antirachitic potency of vitamin D. 



The recognition of vitamin A as a component of cod liver oil was more 

 difficult because of the relatively small concentration of this fat-soluble 

 vitamin. Although the quantity of vitamin A present in this oil is entirely 

 adequate for detection by biological tests or by the antimony trichloride re- 

 action, it is too low to offer a satisfactory source of material for the isola- 

 tion of this vitamin. Actually cod liver oil is a rather poor source of vita- 

 min A. Samples of cod liver oil containing 800 International Units of vita- 

 min A per gram are the ones usually obtained. This is only one two- 

 hundred-fiftieth of the concentration frequently reported in the liver oil of 

 the soupfin shark {Galeorhinus zyopterus). Since crystalline vitamin A 

 possesses a biopotency of approximately 3,333,000 International Units per 

 gram, it is evident that one can expect about a 0.02% concentration of this 

 vitamin in cod liver oil. 



Following the early recognition of the biological effect of deficiency of 

 fat-soluble factors, by Osborne and Mendel, ^~^ and by McCollum and 

 Davis,*"'' and the demonstration of the dual nature of the cod liver oil vit- 

 amins,* chemical and physical methods for the estimation of vitamin A were 

 necessary to replace the laborious and inaccurate bioassay test, before 



1 T. B. Osborne and L. B. iNIendel, /. Biol. Chem., 15, 311-326 (1913). 

 = T. B. Osborne and L. B. Mendel, /. Biol. Chem., 16, 423-427 (1913). 

 ' T. B. Osborne and L. B. Mendel, /. Biol. Chem., 17, 401-408 (1914). 

 ^ E. V. McCollum and M. Davis, /. Biol. Chem., 15, 167-175 (1913). 

 ^ E. V. McCollum and M. Davis, /. Biol. Chem., 19, 245-250 (1914). 

 « E. V. McCollum and M. Davis, .7. Biol. Chem., 20, 641-658 (1915). 

 ^ E. V. McCollum and M. Davis, /. Biol. Chem., 23, 231-246 (1915). 

 s E. V. McCollum, X. Simmonds, J. E. Becker, and P. G. Shipley, J. Biol. Chem., 53, 

 293-312(1922). 



667 



