Only a few years have elapsed since the existence of vitamins was first brought prominently to attention. The claims for the existence of such accessory food factors were received with skepticism for some time, for it seemed unlikely that substances playing a prominent part in nutrition could have escaped recognition so long. Most of the earlier observations and deductions have now been tested repeatedly and found to be correct. Within less than a decade after Funk coined the word vitamin, he felt justified in stating that the subject of vitamins, already beyond the stage of hypothesis, is based on a firm foundation and has received universal recognition. In spite of this, we are well aware, he adds, that great gaps exist in our knowledge, so that we cannot regard the chapter as closed. The skepticism in regard to the existence of such special and unique dietary essentials—substances characterized by a disproportion between the apparent large importance of their functions and the small amounts in which they are ordinarily consumed—has in part arisen from the failure heretofore to isolate and identify the vitamins as chemical entities.…
