214 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



We have now to consider how these two main end products 

 of nitrogen metabolism, viz., urea and hippuric acid, are 

 reabsorbed into the cycle of nature. They are not in them- 

 selves directly available for plant food, and the first stage in 

 their reabsorption by plants, whose nitrogen may serve again 

 as food for animals, consists in their conversion into ammonia. 

 That the conversion of urea into ammonia was a fermentation 

 process, and therefore due to life agency in some form, most 

 probably to bacteria, was first suspected by Pasteur, and also 

 by Tiegheim. Subsequent investigators showed that numerous 

 organisms can induce ammoniacal fermentation. The most 

 active of these is a micrococcus known as Micrococcus urece, 

 and also a bacillus, Bacillus urece. These organisms are very 

 widely distributed, and consequently urine, if left exposed to 

 the air, very rapidly becomes ammoniacal, and the strong smell 

 of an ill-kept urinal is thus accounted for. In normal health 

 it has been shown that these organisms are not present in 

 freshly excreted urine. 



To demonstrate the ammoniacal fermentation of urea, 

 some 50 c.c. of fresh urine may be taken and diluted with an 

 equal volume of water in a conical flask, thus exposing a large 

 surface to the air ; the solution may be infected with a drop or 

 two of ammoniacal urine, or with a few centigrams of garden 

 soil, and allowed to stand with occasional shaking for some 

 days. A similar solution may be made up with similarly 

 infected urine, and a small bottle completely filled with it, 

 and stoppered. Both flask and bottle may be placed in the 

 incubator at a temperature of 26 C. (80 F.) ; in a day or two 

 both solutions, on testing with litmus paper, will be found to 

 have become strongly alkaline, and Nessler reagent will reveal 

 the presence of considerable quantities of ammonia. It is 

 evident from this experiment that ammoniacal fermentation 

 of urea can take place both under anaerobic and aerobic 

 conditions ; the organisms of ammoniacal fermentation 

 belong therefore to the class known as facultative aerobes. 



