Williams (30) brought forward a test for the anti-neuritic principle which at first appeared to be a great step in advance since it promised to detect very small amounts of the substance in a short space of time and with a minimal requirement of material. The test was based on the conception that the yeast cell is unable to grow in a medium lacking in the anti-neuritic substance. It was reported that the growth was in proportion, roughly, to the amount of "vitamin" present. The test was carried out with a hanging drop of culture medium. The number of progeny of a single yeast cell counted after an interval of a few hours constituted the basis of judgment as to the richness or poverty of the solution in the desired substance. Bachmann (31) also described a modification with yeast as the test organism, and Funk (32) described a method for growing larger numbers of yeast cells and measuring their volume by centrifuging in capillary tubes. Unfortunately, this method, which was hailed with great enthusiasm when first described, has proven to be a complete disappointment.