22 THE VITAMINS 



employed interchangeably the existence has now been established of 

 at least two other fat-soluble factors not identical with vitamin A. These 

 are the antirachitic substance now usually called vitamin D,^ and a 

 substance essential to reproduction (though no more so than is vitamin 

 A) which was discovered by Evans and by him at first designated as 

 X, but which is now commonly known as vitamin E. Vitamins D and 

 E were dififerentiated from vitamin A by observed differences in occur- 

 rence, certain physical and chemical characteristics, and definite physio- 

 logical properties without unduly altering the original significance of 

 vitamin A. 



What was formerly known as vitamin B, as explained in Chapters 

 II and III, has ceased to exist as hitherto understood; and to explain 

 the functions previously attributed to it, at least two independent 

 factors must be postulated, neither of which alone fulfills the concep- 

 tion for which the term vitamin B had stood. One of these is the 

 antineuritic vitamin which is also essential to growth, while the other 

 is (or others are) essential to growth as well. This has resulted in 

 considerable confusion in terminology which was not the case in nam- 

 ing the fat-soluble vitamins. 



At first it seemed best, in the interest of clarity, to use two new 

 designations for the two factors into which the old "vitamin B com- 

 plex" had been resolved — "vitamin F" for the antineuritic substance, 

 and "vitamin G" the more heat-stable "Goldberger factor" (described 

 in Chapter III beyond) ; and these designations have been used by some 

 of the scientific bureaus of the United States Government as well as 

 individual American writers, especially during the years 1927 and 1928. 

 Meanwhile, however, the term vitamin F had been suggested in con- 

 nection with a postulated new fat-soluble vitamin which conception, 

 however, was subsequently dropped. Thus the usage regarding the 

 letter F became somewhat confused, and the recent tendency of Ameri- 

 can writers has been to employ the designation "vitamin B" (new 

 style) for the antineuritic substance and continue the use of the term 

 "vitamin G" in the sense indicated above and developed in Chapter III ; 

 while the British have suggested the tentative use of the terms Bi, B2, 

 etc., to designate the different nutritionally essential substances of the 

 original vitamin B complex. As will appear in Chapters II and III 

 there is now abundant evidence of the existence of more than two such 

 substances. 



As the vitamin theory of the present day has so largely grown out 



^ The term vitamin D has also been applied by some writers to the substance generally 

 known as bios, which is characterized by its accelerating influence upon the growth of yeast. 

 Bios has been quite fully discussed by Tanner (1925). 



