264 Prof. Potter. Electrical Effects accompanying the [July 14, 



seat of the chemical action became changed and the direction of the current 

 was always reversed. 



We may now proceed with some typical examples of the results obtained 

 with experiments undertaken first with yeast. 



Various Concentrations of the Medium. 



With the ordinary standard of 5 grm. of yeast at a temperature of 25° C. 

 and a 10-per-cent. solution of glucose an E.M.F. of 0'32 volt was registered 

 in the course of 7 minutes, after which the voltage gradually declined until 

 at the end of 40 minutes it was - 25, at which figure it remained fairly 

 constant for a further period of 50 minutes. A reference to fig. 2 shows the 

 variations of the voltage with solutions of different degrees of concentration. 



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Fig.2 





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,-.-307° 

 — 40°/' 













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507" 



io 20 30 40 Time so in 6ominures70 ao 



Curves showing development of E.M.F. in 5, 10, 20, 30, 40, and 50 per cent, solutions of 

 glucose. 5 grm. of yeast employed in each case. Initial temperature 25° C. 



With 20-per-cent. glucose the maximum voltage, 0-32, was reached in 

 10 minutes ; with 5-per-cent., 15 minutes was occupied in reaching a 

 maximum of - 31. The 10-per-cent. thus appeared to be the best mean, but 

 it will be seen that the concentrations of 5, 10, and 20 per cent., though 

 varying slightly in their initial rapidity of action, attained a very similar 

 voltage, and the curve thereafter followed much the same course. With 

 30-per-cent. glucose there was a slower development, the maximum voltage, 

 which was - 26, being attained only after 23 minutes, while with still higher 

 degrees of concentration a markedly slower action and lower voltage indicated 

 a solution much less favourable to the development of the yeast. Thus 

 40,-per-cent. glucose registered only 0'18 volt after 90 minutes, and 50-per- 

 cent. 0'08 after the same period. 



