11-9 



THE YEAST CELL 



Saccharomyces which require from 3 to 12 days to ferment galac- 

 tose in a Durham tube with galactose yeast extract agar. We have 

 encountered similar slow fermenters of galactose and Mr. B. D. 

 Mundkur has undertaken a study of them. These cultures when in- 

 oculated into a Smith tube (fig. 11-3) containing 4 per cent galactose 

 and the medium described on page 11-7, produce gas in the inverted 

 insert«in from 5 to 20 days. This is undoubtedly the same phenome- 

 non described by Winge and Roberts. They found in addition that 

 after fermentation had occurred, the fermenters could be "deadapted" 

 by transfer to maltose broth and were "readapted" by transfer back 



ferl 



GAS 



Fig. 11-2 Fermentation in Durham Fermentation Tubes. 

 Growtli oi yeast occurs in nutrient broth and results in accumula- 

 tion ot carbon dioxide in the small inverted tube. A complete 

 nutrient with only a single carbohydrate source is used. This is 

 the test used by Lindegren and Lindegren. It depends on the 

 growth ot yeast to a sufficient amount to produce gas more rapid- 

 ly than ditfusion from the medium can occur. A small inoculum 

 increases during the process; the growth of the yeast depends on 

 the presence of air so tlie test is not anaerobic. 



to galactose broth. They interpreted this result as indicating that 

 each cell produced a small amount of enzyme and that the popula- 

 tion as a whole slowly achieved or lost fermentative ability. 



