250 MICRO-ORGANISMS AND FERMENTATION. 



in certain respects ; Pasteur in so far as zymase can only be 

 produced by living cells, Liebig in so far as the fermentation 

 is excited, not by living cells, but by a separate enzyme. 



Thus, for the first time, we have a solid basis for a true 

 theory of fermentation established by the study of that par- 

 ticular enzyme which brings about fermentation. A short 

 resume is given below of the properties of the enzyme, so far 

 as they have been clearly defined in the short space of time 

 succeeding its discovery. It must, however, be understood 

 that very little is known concerning its chemical character. 



Zymase cannot be regarded as consisting of living matter. 

 It can be distinguished from invertase of yeast cells, which 

 converts saccharose into fermentable sugar, by the fact that 

 it does not diffuse through the cell wall. 



If the juice is heated to 40-50 C., a flocculent pre- 

 cipitate of albumen forms, and the clear liquid loses its fer- 

 mentative power. Invertase has been identified in yeast- 

 juice, and it must also contain an enzyme hydrolysing maltose 

 and one hydrolysing glycogen, as it is capable of bringing 

 about fermentation with these carbohydrates, neither of them 

 being directly fermentable ; but, according to Hahn, it also 

 contains a substance of importance, a proteolytic enzyme 

 hydrolysing albumen. If a test tube containing fresh yeast- 

 juice, and another containing juice that has stood for a week 

 at room temperature in presence of toluol (to prevent the 

 growth of micro-organisms), are placed in a water-bath at 

 40-45 C., it will be found that in the former a strong 

 coagulum separates out in a few minutes, whilst in the latter 

 only a few flocculent particles are visible. The coagulable 

 albumen, when kept for some time, disappears by a species 

 of auto-digestion. Hahn has named the enzyme yeast- 

 endotryptase. This enzyme reacts best in presence of acid, 

 whilst the activity of zymase is improved by the addition of 

 weak alkali. The presence of oxygen is advantageous to proteo- 

 lysis. The enzyme can be isolated in a comparatively pure state, 

 and is found in yeast cells. According to Hahn, it cannot be 

 separated from quite normal cells, and such cells can only deal 

 with those albuminoids which are forced through the cell walls. 



Endotryptase has a powerful action on zymase, and even 



