30 MICRO-ORGANISMS AND FERMENTATION. 



selves to poisons. By long-continued cultivation it has proved 

 possible to introduce large quantities into nutritive substrata, 

 and at the same time it has been noted in several cases that 

 a marked change of character takes place. It has, however, 

 proved impossible to fix these newly acquired characters ; they 

 are of a purely transitory kind. As soon as the poison is 

 removed the growth reverts to its original character. From 

 the numerous examples, we select the following : Galeotti 

 accustomed Bacterium prodigiosum to grow on a 2 per cent, 

 carbolic acid nutritive gelatine. Pulst accustomed Penicillium 

 glaucum to withstand continually increasing quantities of 

 poisonous copper salts, whilst its conidia germinated more 

 rapidly than usual. 



The results obtained by accustoming yeasts to the presence 

 of certain poisons are of special interest in the technology of 

 fermentation. For example, the yeast in distilleries may work 

 in a mash which by treatment with a disinfectant has been ren- 

 dered more resistant to bacteria, a process which takes the place 

 of the usual souring with lactic acid. For this object sulphuric 

 acid, hydrochloric acid, and hydrofluoric acid have been made 

 use of. Effront proved that much smaller quantities of hydro- 

 fluoric acid were required than of the other two. In considera- 

 tion of the different extent to which the yeasts are attacked 

 by the hydrofluoric acid (or fluorides), Effront tried by special 

 cultivation of yeasts to accustom them to work in a mash 

 which contained so much of the reagent that the bacteria 

 were suppressed. He found that the addition of 300 mgm. 

 of hydrofluoric acid to 100 c.c. of liquid completely inhibited 

 the growth of yeast, whilst its fermentative activity was only 

 restricted. If, however, the yeast is gradually accustomed to 

 the poison, beginning, for example, with 20 mgm. per 100 c.c., 

 and rising by degrees to greater doses, a race of yeast will 

 be formed that can multiply even in presence of the original 

 dose. In presence of 200 mgm. per 100 c.c. the fermentative 

 power of the yeast is increased, according to Effront, if it is 

 introduced into a mash which also contains fluorides. In 

 practice about 10 grammes of hydrofluoric acid are used for 

 every hectolitre of mash. Even if this process succeeds in 

 suppressing bacteria in the mash, which is not always the case, 



