134 BACTERIA. 



lactic acid fermentation ever takes place. Although this is 

 true in a certain degree, it is found, as has already been 

 stated, that there are actual differences in degree as to the 

 readiness with which the various sugars undergo the alco- 

 holic and lactic fermentations. For instance, although the 

 glucoses are readily converted into lactic acid, the saccharoses, 

 which are specially fermentable by the saccharomyces, are 

 not very easily transformed into lactic acid ; whilst, on the 

 other hand, sugar of milk, which does not readily yield 

 alcohol, may be comparatively easily converted into lactic 

 acid. Muscle sugar and mannite, neither of which can be 

 converted into alcohol, may both be broken up into lactic 

 acid, as may all those substances that are specially affected 

 by the butyric fermentation. 



It was for some time thought that the fermentation of 

 urea, through which carbonate of ammonia is frequently met 

 with in the urine, was the result of a single micrococcus, the 

 micrococcus ureae, a small organism about i/* in diameter, 

 which may occur in pairs, in tetrads, or in longer chains, and 

 which, in the presence of suitable nutrient materials, and of 

 urea, either in artificial solution or in urine, determines a 

 regular hydration of these substances and their conversion 

 into carbonate of ammonium. 



Since the time of Pasteur's researches, however, Leube 

 has found an organism about double the size of the above 

 and arranged in chains, which rapidly decomposes solutions 

 of urea into carbonate of ammonia. It differs, too, from 

 Pasteur's organism in that it peptonizes or digests gelatine, 

 causing it to liquefy, and it appears that, unlike some 

 other bacilli and sarcinae that can set up a feeble urea 

 fermentation, it is quite as powerful an ammoniacal ferment 

 as the small micrococcus ureae described by Pasteur, as in 

 both of them the fermentation can go on most vigorously, even 

 in the medium that has become distinctly alkaline, z>., the 

 carbonate of ammonia accumulates until about 13 per cent, 

 of this substance has been formed ; these two microbes may 

 be said to bear the same relation to the other urea-forming 

 bacteria that the Saccharomyces cerivisise and the other 

 more powerful alcohol-forming yeasts have to the weak 

 saccharomyces and other sugar fermenting organisms. 

 That this power is not confined to a single organism is not 

 remarkable, since it is quite possible by boiling the urea in 



