ENZYMES AND OTHER FERMENTS DIGESTION. 133 



(NH 2 ) 2 CO + 2H 2 O = (NH) 2 CO 3 . 



The agency concerned in this addition of water molecules was 

 for a long time in doubt, but investigation finally showed it to 

 be a case of ferment action. In all urines undergoing this 

 change numerous bacteria are present and by separating and 

 making pure cultures of these, several species have been found 

 which are capable of decomposing pure solutions of urea. 

 The name micrococcus urea has been given to one of the most 

 active of these bacterial organisms. It has been found, how- 

 ever, that the action is certainly due to a soluble product or 

 enzyme secreted by the bacteria, since it may be brought into 

 solution. This solution, after the most careful filtration even, 

 is very active when properly made and will quickly induce the 

 ammoniacal decomposition in urea solutions. 



The name urease has been given to this soluble ferment, 

 which must belong to the hydrolytic group. It is active up 

 to about. 50 C. and is much more stable in presence of alka- 

 lies than with acids, as would be supposed from the reaction 

 it produces. The enzyme is not readily extracted from the 

 living bacterial cells; these must first be destroyed or allowed 

 to die out in process of making strong cultures. The cells 

 holding this enzyme are very widely distributed in nature, 

 being found in the air, in most soils and in river water. This 

 accounts for the usually rapid fermentation of urine. 



B. OXIDATION REACTIONS. 



Under the head of oxidation reactions it is very easy to 

 include some in which the essential phenomenon is clearly one 

 of addition of oxygen to the decomposing substance. This is 

 certainly the case in the production of acetic acid from weak 

 alcohol. In other cases, however, the actual nature of the 

 chemical change which occurs is more obscure and the classi- 

 fication of such reactions as oxidation reactions is possibly open 

 to doubt, as will appear below. 



