A group of closely interrelated vitamins found in rice bran, yeast, wheat germ, etc., originally thought to be one substance. Studies carried out by R. J. Williams and associates later revealed the astonishing complexity of this group. He states as follows: “The physiological activity originally observed was due to the additive effect of a considerable number of substances, each one of which is of itself essential. If and when the designations B1, B2, B3, etc., are used, they have an entirely different meaning from the parallel use of D1, D2, D3 orK1 and K2 because in the case of theD and K vitamins one form can replace another. In the case of the B vitamins each form is a distinctly different substance with different functions, and each member of the family is separately indispensable.
