SUPPLEMENT 71 



produced, from mannite and dulcite, also ethyl-alcohol, acetic, formic and 

 lactic acids, and even succinic acid. We have thus established a fermentation 

 for all these alcohols, and we may add that glycerine as well is known frequently 

 to undergo fermentation. 



Having referred to the most important non-nitrogenous organic materials 

 which may be employed in fermentation, we must now turn to nitrogenous 

 bodies. Plants, as we have already seen, are very economical of nitrogen ; 

 it is only when they are provided exclusively with substances rich in nitrogen 

 that they give off that element in the form of ammonia. On the other hand, 

 the excrement of animals always contains nitrogen, and in urine specially it is 

 present in the form of urea, uric and hippuric acids. It has long been known, 

 however, that these substances do not form suitable sources of nitrogen for 

 autotrophic green plants, and hence it is all the more important that they should 

 undergo transformation in the soil. In this process micro-organisms are con- 

 cerned to a very large extent. Best known of all is the transformation of urea 

 into ammonium carbonate, a process often termed ' urea-fermentation '. It 

 takes place according to the formula : 



CO(NH 2 ) 2 + 2H 2 O = CO,(NH 4 ) 2 



Here we have simply a taking up of water without any splitting, just like 

 what occurs in so many enzyme actions. Since the gain in energy in this process 

 is but limited, the formation of ammonia has, perhaps, rather the effect of 

 making the medium alkaline, and so rendering the substratum unsuitable for 

 other organisms. Still it is true that Uro-Bacteria are not very resistant to 

 ammonia. Urea fermentation is, however, not the only source of energy to 

 these Bacteria, for they are all strongly aerobic. A metabolic utilization of the 

 ammonia so formed is not known ; still one must not imagine that ammonia 

 arises here in the same way as it does in genuine peptone nutrition. Since 

 the urea does not serve as a source of carbon to the Uro-Bacteria, they cannot 

 exist when supplied with it alone (BEIJERINCK, 1901) ; it serves as a source of 

 nitrogen only. As regards their carbon requirements the various forms behave 

 differently ; those species which get on with acetic acid or oxalic acid make 

 the most moderate demands, but they form only a little ammonium carbonate. 

 More arises from such forms as grow in tartaric acid, and more still from those 

 which employ malic acid. The greatest amount of ammonia is formed by 

 Urobacillus pastenrii and Urococcus ureae, which employ meat extract as the 

 source of carbon, for if a trace of them be added to the culture they can in a few 

 days completely transform 10-12 g. of urea in 100 g. of fluid. The immediate 

 cause of the formation of ammonia is an enzyme, urease, as to whose presence 

 or absence there has been much controversy. Its existence cannot be doubted 

 after BEIJERINCK'S recent discoveries, for this authority was able to show that 

 Bacteria which had been killed by chloroform could attack the urea just as well 

 as the living ones ; he showed also that urease cannot diffuse out of the cells, 

 so that the previous statements as to ' soluble urease ' must be attributed to 

 minute Bacteria overlooked in the fluids under consideration. From uric acid 

 ammonia at least arises ; the fate of the hippuric acid we need not consider 

 (comp. MIQUEL in LAFAR'S Mykologie, III. 71, as to that point, and also as to 

 the morphology of Uro-Bacteria). 



Another nitrogenous product, widely distributed in the animal kingdom, 

 and also present in Fungi, is chitin. BENECKE (1905) has isolated a Schizomycete 

 which is able to break down this exceedingly resistant body, although certainly 

 only when well nourished and in presence of air. 



The greatest interest centres round the nitrogenous bodies known as 

 proteids, which are available for use by micro-organisms on the death of any 



