1911.] Substances upon the Autofermentation of Yeast. 457 



Other instances of the same effect are the following, all of which refer to 

 10 grm. of yeast : — 



Table XIII.— Effect of Toluene. 



3.2.08 

 10.9.09 

 17.9.09 

 17.10.07 

 20.10.07 



Water + toluene. 



As in the case of salt solutions the rate slowed down comparatively soon, 

 owing to exhaustion of the fermentable material. The effect is not due 

 to a specific action on the enzymes, since toluene has either no effect or a 

 slight inhibitory effect on the autofermentation of yeast-juice, as is shown 

 by the following result : 25 c.c. of yeast-juice in three hours gave 403 c.c. of 

 C0 2 ; in presence of 5 c.c. of toluene the same volume of yeast-juice gave 

 34 c.c. 



It is, however, not impossible that this result may be explicable on the 

 ground of plasmolysis. In spite of the small solubility of toluene in water 

 a considerable degree of plasmolysis is observed when yeast is shaken with 

 water and excess of toluene. Further experiments on this point are in 



(5) With regard to the possibility that the foregoing changes may be 

 ultimately due to the action of hormones in the manner suggested by 

 H. E. and E. F. Armstrong (7) no very definite conclusion can be drawn. 

 The action of toluene on yeast undoubtedly presents the closest analogy to 

 that which it exerts on the Aucuba leaf, and it cannot be denied that the 

 various salts employed do penetrate at all events into the outer layers of the 

 yeast cell. Several of the phenomena, however, appeared to be difficult to 

 explain in this way, especially the lack of action of a substance like urea, 

 which penetrates the cell, and the causation of the phenomenon by simple 

 drying. In any case the acceleration caused by salts is accompanied by 

 concentration of the cell contents, so that dilution cannot in these instances 

 be the effective cause, as suggested by Armstrong* for the phenomenon 

 observed by him. 



3. Effect of Alcohol on Autofermentation. 

 The plasmolysing effect on yeast of solutions of alcohol was found to be 

 practically absent from concentrations up to 10 per cent, (rather more than 

 * Loc. cit. 



