336 APPLIED BACTERIOLOGY 



the ' keeping ' of the finished product, which is generally 

 kept for a year in order that the flavour may fully develop. 



2. Fermentation by Hydration. — The most important fer- 

 mentation process which falls under this head is the con- 

 version of urea into ammonium carbonate by the action of 

 the Micrococcus urece. 



Animoniacal Fermentation of Urea. — Freshly-passed urine 

 is faintly acid in reaction, and contains about 3 per cent, 

 of urea, but is free from ammoniacal salts. On standing, 

 however, the urea disappears, and ammonia is formed, and 

 the urine becomes strongly alkaline in reaction. Liebig, 

 who attempted to find the cause of this change, came to 

 the conclusion that it was due to the presence in the urine 

 of decomposing particles of the mucous membrane of the 

 bladder. Pasteur and Van Tieghem found, however, that 

 all ammoniacal urine contained an organism, which brought 

 about this change, which they called the Torula urinw, but 

 which is now generally known as the Micrococcus ureoe. 

 The change this organism brings about in the urine may 

 be represented by the following equation : 



CO(NH2)2 + 2H20 = CO(NH40)2. 



IJrea. Ammon. 



carbonate. 



The Micrococcus urece is generally seen in pairs, tetrads, 

 and in chains which are often of considerable length. The 

 cocci vary from 0'8 to 1-0 /j, in diameter ; but, according to 

 Jaksch, it sometimes exhibits a more or less bacillary 

 form. On gelatine plates, the M. urece appears after 

 twenty-four hours as white pearl-like colonies, which after 

 some time become like drops of tallow. The gelatine is 

 not liquefied. The alkaline reaction resulting from the 

 ammoniacal fermentation of urea does not seriously inter- 

 fere with the growth of the organism, which will grow in 

 the presence of up to 18 per cent, of ammonium carbonate. 



