also improved his original method and devised a gravimetric method for the same purpose. From the viewpoint of methodology we now have methods which are suitable as quantitive procedures for determining the effect of extracts of unknown substances on yeast growth and hence if the stimulatory substance is vitamine "B," a means of determining within a space of twenty-four hours the approximate content of stimulatory material in a given source. Since the Funk method is the simplest of these and illustrates the principles involved it will suffice to describe that. _Funk method of yeast test with Eddy and Stevenson modification_ 1. To a basal diet of 9 cc. of sterile culture medium such as a von Nageli solution [Footnote: von Nageli's solution consists of the following ingredients NH_4NO_3, 1 gram; Ca_3(PO_4)_2, 0.005 gram; MgSO_4, 0.25 gram dextrose 10.0 grams made up to 100 cc. with distilled water. Other culture media may be used and such combinations will be found in any text on yeasts. They all permit a certain amount of growth but all are apparently stimulated by the addition of vitamine extracts.] in a sterile test tube is added 1 cc. of the sterile, neutral, watery extract of the source of the vitamine. A pure culture of Fleischman's yeast (Funk prefers brewer's yeast) is maintained on an agar slant and twenty-four hours before the test is to be made, a transplant is made to a fresh agar slant. One standardized platinum loopful of the twenty-four hour yeast growth is then used to inoculate the contents of the tube, the tube stoppered with cotton and incubated for from twenty-four to seventy-two hours at a temperature of 31°C. The seventy-two hour incubation period yields nearly optimum growth for this purpose. 2. At the end of this time the yeasts are killed by plunging the tube in water heated to 80°C. and maintained at this temperature for fifteen minutes. The contents of the tubes are then poured into a Hopkins centrifuge tube which has a capillary tip graduated in hundredths of a cubic centimeter. After twenty minutes centrifugating at a speed of about 2400 revolutions per minute the yeasts in the solution have all been packed into the tip and the volume can then be read accurately to thousandths of a cubic centimeter (with the aid of a scale and magnifier). With a control tube containing 9 cc. of the sterile media and 1 cc. of distilled water in place of the 1 cc. of extract a comparison can be obtained which is an accurate measure of the stimulatory effect of the extract. If this stimulus is due purely to vitamine it is obvious that this procedure would enable us to compare extracts of known weights of and arrive at comparisons which would be measures of their vitamine content. In other words the procedure is now in a satisfactory form for testing and its value depends merely upon our ability to show that the stimulus given the yeast is due solely to vitamine "B."