36 PHYSIOLOGY OF BACTERIA 



They are brought about by a chemical compound 

 (zymase), which is produced by the cell and which, 

 after once having been produced, acts independently 

 of the cell. The cell may control to a certain extent the 

 amount of enzyme produced, but the action of the enzyme 

 once produced is beyond the control of the cell. The 

 enzyme follows always the laws of enzyme action, even 

 if it should be against the vital interests of the cell. The 

 fermentation of sugar to alcohol and carbon dioxide will 

 continue for some time after the multiplication of yeast 

 cells has ceased; there is already too much alcohol 

 present to allow growth, and very little energy is needed 

 by the resting cells, yet the enzyme is present, and it 

 continues to act until it is checked by the maximum 

 amount of alcohol, or by the disappearance of the sugar. 

 This is against the best interests of the cell (as we 

 understand them), but is in accordance with the laws 

 of enzyme action. Another example is the excessive 

 heat production by vinegar bacteria mentioned before. 



(6) THE KNOWN ZYMASES OR FERMENTING ENZYMES 



Urease. — The oldest known zymase is doubtless the 

 urease discovered in 1876 by Musculus who noticed it 

 in the slimy urine of some patients and believed the 

 enzyme to be of human origin. Miquel (1904) sum- 

 marizes his own earlier experiments in the statement 

 that cultures of urea bacteria can be brought to the 

 point where they decompose in one hour 100-120 gm. of 

 urea per liter of culture. 



Such cultures can be filtered through porcelain filters without 

 much loss of urease if large amounts of culture are used. From this, 

 it would seem that the urease were no endoenzyme. This is very- 

 improbable however because the cells would derive no benefit from 

 urease outside of the cell. It is more probable that a large number of 



