THE CHEMISTRY OF BACTERIA. 107 



ous substance, it-mav not be without effect when formed in 

 the tissues, in disease conditions. 



An interesting fermentation of this type is occasion- 

 ally met with in urine. Bacteria, when introduced into the 

 bladder, either as the result of an injury, or by the use of 

 instruments or otherwise, may develop and give rise to fer- 

 mentative changes. Usually an ammoniacal decomposi- 

 tion results, but at times the urine remains strongly acid 

 and possesses a marked odor of hydrogen sulphide. This 

 condition, or hydrogen sulphide fermentation of the urine, is 

 known as hydrothionv/ria. A number of bacterial species 

 have been isolated by the author and by others from such 

 urines, and when inoculated into sterile, normal urine they 

 promptly produce this gas. The so-called "neutral" sul- 

 phur compounds of the urine, and not the sulphates, are 

 acted upon. Hydrogen sulphide is a common product in 

 the decomposition of protein substances. The odor of 

 rotten eggs is due to this gas. 



Ammoniacal fermentation of urine. — Normal urine is per- 

 fectly free from bacteria for reasons heretofore given (p. 65). 

 When bacteria are introduced into the bladder, in some way 

 as mentioned above, they usually induce a marked ammon- 

 iacal decomposition. The urea undergoes hydration, form- 

 ing ammonia and carbonic acid, which, of course, unite to 

 form ammonium carbonate. The same fermentation will 

 almost invariably occur when normal urine is allowed to 

 stand for some hours at a warm temperature. The change 

 corresponds to the equation: 



CO(NH2)2 + HjO = 00^ + 2 NH,. 



Urea. 



Pasteur designated the cause of this fermentation as 

 the Micrococcus urece. The change, however, is not spe- 

 cific, due to a single organism, but can be induced by a 



