The Yeast Test. 



139 



2. A report of the result of 284 determinations on varying 

 dilutions of an extract of alfalfa meal which in its highest concen- 

 tration contained the extract of 400 grams of meal in 1,000 c.c. of 

 water. This shows that the curve of stimulation is a curve with a 

 definite shape which rises steeply from the control point to an 

 optimum and then gradually declines to the right of the optimum. 

 It also shows that there is greater variability in the region to the 

 right of the optimum in the individual determinations. These 

 results indicate clearly that if vitamine B is a factor in the test it is 

 only one of several and that critics of the test are right in saying 

 that comparisons cannot be made between the extracts of equal 

 weights of extracted material at the present itme. 



3. A series of studies on other sources showing that dilution 

 produces similar results to those in alfalfa extracts but that the 

 optima and shape of the curve of stimulation differ with each 

 substance tested though in general they show a steep rise, an 

 optimum and in some cases a decline to the right of the optimum. 

 These results confirm the conclusions of 2 and make clear that it 

 will be necessary to find a basal diet for yeast which is optimum in all 

 except vitamine before the results of tests can be made comparative. 

 In the group of tests presented in this connection were included 

 extracts of pancreas and other organs made with acidified and 

 with neutral alcohol. The results fail to confirm the contentions 

 of Swoboda 1 in regard to failure of pancreas to yield the test or to 

 support his vitaminogen speculation. 



4. Experiments are given to show that when the Medium F 

 of Fulmer, Nelson and Sherwood 2 is substituted for Nageli solution 

 in the alfalfa series the control values are markedly higher but 

 that the alfalfa extract still exerts a stimulatory influence in every 

 concentration used. These results fail to confirm their contention 

 that the stimulatory effect is due purely to salt optimum and 

 quality. They do indicate that the yeasts are extremely sensitive 

 to such salt concentrations and that vitamine B is not the only 

 factor in the test. 



5. Experiments are presented to show the effect of alkali on 

 the stimulatory power of the test. In every case we obtained a 



1 Swoboda, F. K., J own. Biol. Chem., 1920, xliv, 531. 



2 Fulmer, Nelson and Sherwood, Journ. Am. Chem. Soc, 1921, xliii, 186 and 191. 



