1911.] 



Decomposition of Organic Compounds. 



267 



when the organism is employed in a more effective strength. It was also 

 found that the gradient of the curve indicating the growth of potential is 

 very steep when the yeast is introduced into a solution of glucose at the 

 optimum temperature, but the curve is much less steep when the tempera- 

 ture approaches the limits of the maximum or minimum for the organism. 

 At the minimum temperature, 0° C, and at the maximum, 50° C, no E.M.F. 

 is produced, and it is important to note that a difference of potential is only 

 found within the limits at which the various organisms can live. 



The maximum voltage recorded with yeast and glucose or cane sugar was 

 0*3 — 0*4, and a voltage of this order was never exceeded in any of the 

 experiments under any of the conditions tried. When battery cells of a 

 larger capacity, containing 1\ to 2 litres, were used, it was found that no 

 difference could be detected in the amount of the E.M.F. registered, and the 

 voltage thus bears no relation to the volume of the fermenting liquor. It 

 appears also that the voltage is quite independent of the thickness of the 

 platinum wire or the surface of the electrode, thus when pieces of platinum 

 foil up to 1\ cm - square were welded on to the platinum wire, the voltage 

 remained the same. 



A small current can always be detected in the yeast-glucose cells, and the 

 voltage as registered by metallic conductors is due to the charge collected 

 in the fermenting liquid. When a short circuit is made by joining the leads, 

 the liquid in the neighbourhood of the electrodes is at once discharged, and 

 the voltage is considerably reduced. But when the leads are again separated 

 the E.M.F. gradually increases as the liquid recovers its charge through the 

 activity of the yeast cells, and it becomes once more fully developed in a 

 time varying according to the species of organism and the cultural con- 

 ditions. Fig. 5 shows the effect of a short circuit in diminishing the E.M.F. 



10 20 30 40 50 60 70 80 90 



Time in minutes. Cell short-circuited at times indicated by arrows. 



