The "vitamin" hypothesis of Funk postulated the existence of a number of unidentified dietary essentials, each of which acts as a protective substance to the organism. Accordingly, the lack of one or another of these was believed to lead to the development of a specific syndrome; in one case it was beriberi, in another scurvy, in another pellagra. Even rickets and less clearly defined failures of nutrition were brought into the range of possible explanation. In this sense the expression "deficiency disease" has become popular; and the lack of some necessary though undemonstrated food factor became a satisfying though vague explanation that is readily accepted by the uncritical.
There seems to be no doubt at present of the actual existence of deficiency diseases in the original sense in which this expression was used, that is, a syndrome due to the absence of a specific as yet unidentified food factor. For