28 MICRO-ORGANISMS AND FERMENTATION. 



have the power of killing germs, they do not destroy enzymes. 

 This fact has proved of importance in advancing recent studies 

 of enzymes, etc., where it is necessary to inhibit the action of 

 micro-organisms on the susceptible liquids employed. R. 

 Koch first proved the antiseptic action of ether and alcohol, 

 and recent research has brought to light the interesting fact 

 that it is not absolute alcohol, but a 50 to 60 per cent, alcohol 

 that exhibits the strongest disinfecting power. This may be 

 explained by supposing that absolute alcohol absorbs moisture 

 from the surface of the cells, and, therefore, makes them more 

 resistant. The vapour of 75 per cent, alcohol appears to be 

 equal in its action to a current of steam, and a still more 

 powerful action is exhibited by a mixture of alcohol vapour 

 of this strength with formaldehyde vapour. The mixture 

 may be used to disinfect fabrics which would suffer by ex- 

 posure to a temperature of 100 C. 



Carbolic acid (phenol), which plays an important part in 

 medicine as a powerful antiseptic, cannot be applied in the 

 fermentation industry, owing to its penetrating odour, but 

 owes its interest to the fact that it does not attack enzymes. 

 On the other hand, a whole series of compounds, of which 

 carbolic acid is a component, are made use of in practice. 



The raw materials of the fermentation industry (rye, 

 wheat, barley, etc.) contain peculiar compounds which, accord- 

 ing to the researches of Jago, Delbriick, Lange, Henneberg, 

 Hayduck, and Seyffert, act as poisons to yeast, and these are 

 assumed to be of an albuminoid character. This action may 

 be observed in the crushed grain or in an aqueous extract if the 

 yeast is added in presence of sugar dissolved in distilled water. 



In their reaction to such influences, the yeast species do 

 not behave uniformly. Thus, under certain conditions a 

 stimulus may be given to some species, whilst under other 

 conditions the poisonous substance may act destructively 

 even in minute doses. Such is the case with the poisonous 

 body present in rye bran, and also with that contained in a 

 dilute hydrochloric acid (0-1 per cent.) extract of wheaten 

 flour, in their action upon brewer's yeast, whilst with the 

 addition of calcium carbonate, soda, gypsum, etc., the action 

 of these reagents on the yeast is prevented. 



