Souza and McCol-lum (33) attempted to make use of yeast cell growth as a test for the anti-neuritic principle (water-soluble B), and showed that no confidence could be placed in it. In the first place, it was found that yeast could grow slowly in a "vitamin"-free medium, and in the second place that the addition of extracts of natural foods which had been so treated as to destroy the anti-neuritic substance completely, were just as effective in stimulating the growth of yeast as were other extracts which did contain the dietary principle. MacDonald and McCollum then carried out an extensive series of transplantations of pure cultures of yeast in a nutrient medium containing no trace of water-soluble B (34). As a result they showed conclusively that a steady growth, through many successive seedings, is possible in the absence of the substance for which it had been suggested the growth of yeast could be made a specific test. Fulmer, Nelson and Sherwood (35), almost simultaneously published data fully in accord with that of Souza, MacDonald and McCollum, and drew the conclusion that the yeast test has no specificity whatever. We are, therefore, again thrown back upon the test for water-soluble B, described by McCollum and Simmonds, as the only one yielding results of any significance.