INTRODUCTORY
Vitamin was first isolated from rice polishings in 1911 by Casimir Funk and shown by him to be the agent which prevented beriberi. It was also in this year that Mendel and Osborne did their comprehensive work on the feeding of single purified proteins to white rats. In the latter work it was established that in addition to nutrients the diet of a growing rat demanded the presence of certain substances hitherto unknown, and which these workers found present in protein-free milk and in centrifuged butter fat. Funk had meanwhile not only extended his isolation of vitamin to other substances than rice polishings—among them yeast—but had shown that aside from the effect on polyneuritic conditions the vitamin was an essential factor in growth stimulation. From these beginnings the development of the importance of vitamin as a growth factor has been rapid. Of all the studies,