1911.] Substances upon the Autofer mentation of Yeast. 455 



Table IX. — Showing Diffusion of Urea into the Yeast-cell. 





Initial 

 yeast. 



Initial 



Final 



Pinal 



P = grm. 



100 grm. 

 ■water 

 within 



the cells. 



?! = grm. 

 urea per 

 100 grm. 



outside 

 the cells. 



K = P/Pi. 



Solids other than 

 urea 



grm. 

 32 -50 



67 -50 



grm. 



5-94 

 94-06 



grm. 

 31 -61 



2-50 

 72-49 



grm. 

 0-85 



3-45 

 89 -10 



3-43 



3-87 



0-89 



Water 





Total weight... 



100-00 100-00 106-60 



93 -40 



Removal of Water by Partial Drying. — If the acceleration of the enzymic 

 activity were due simply to concentration within the cell, removal of water 

 by drying would be expected to produce the same result as removal of water 

 by plasmolysis. In order to investigate this 10 grm. of pressed yeast which 

 had been passed through a 3 mm. sieve were placed in a fermentation flask 

 and subjected to a current of air for 20 minutes. This flask and a control 

 were then connected with the gas-measuring apparatus and warmed in the 

 water-bath at 25°. The rate of autofermentation was considerably increased 

 by this simple method of removing water. 



Table X.— Effect of Partial Drying by Air. 



Time, in mins. 



Cubic centimetres of carbon dioxide given by 

 10 grm. yeast. 



After 20 minutes blow. 



Control. 



15 



14 -5 



4-3 



30 



27 -5 



8-9 



45 



36 -4 



13-3 



65 



43 -6 



18-4 



85 



47 -8 



23-4 



In another experiment three lots of 10 grm. of pressed yeast were weighed 

 out, of which B and C were dried in a vacuum desiccator for two and four 

 hours respectively, whereby B lost 2 grm. and C 3"2 grm. of water. The 

 rate of autofermentation of these samples was compared against A as 



