ENERGY SUPPLY OF THE CELL 



147 



living cells in which the enzyme can be regenerated can 

 be proved only by direct experiment. Such experiments 

 were carried out by the author with compressed yeast, 

 as a simple source of large quantities of cells. 



Different amounts of yeast were placed in flasks containing 100 

 c.c. of a raisin decoction to which 25% sucrose and 2% dried yeast 

 were added. These flasks were closed by a fermentation valve sealed 

 with concentrated H2SO4 which permitted the CO2, but not the 

 moisture, to escape. These flasks were weighed daily. The loss 

 in weight is carbon dioxide. After the weight had become constant, 

 the alcohol was determined by the density of the distillate. 



The results of two such experiments computed for 

 100 c.c. of moisture are shown in Table 31. Starting 

 from the lowest yeast concentration, the amounts of 

 alcohol and carbon dioxide are constant until 0.6 

 gm. yeast is reached. This indicates that the smaller 

 amounts of yeast will multiply to about 0.6 gm. When 

 more yeast was added, the amounts of alcohol and CO2 

 produced increased very distinctly. 



The same result can be obtained with lactic strep- 

 tococci. A culture of Strept. glycerinaceus was grown 

 for twenty-four hours in a well-buffered lactose broth, 

 and centrifugated after neutralization. The bacteria 

 from 1,000 c.c. of culture were put into 100 c.c. of sterile 



