216 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



The ammoniacal fermentation belongs to an increasing 

 number of such changes, which can ultimately be referred to 

 the activity of a non-living enzyme. In 1874 Musculus found 

 that if ammoniacal urine was filtered through filter paper, 

 and the filter paper was washed and dried and afterwards 

 placed in a neutral solution of urea, ammoniacal fermentation 

 took place. This also happened if the filter paper was washed 

 with strong alcohol, showing that the activity was due to 

 something other than the living organism. Although not 

 absolutely conclusive, the evidence at present available 

 indicates that the micro-organisms secrete an enzyme which 

 has been termed urease ; it can be precipitated by alcohol 

 and is destroyed by acids. Sheridan Lea in 1885 obtained 

 a rapid ammoniacal fermentation of a 2 per cent, solution of 

 urea, by incubating it at 38 C. with the alcoholic precipitate 

 obtained from pathological urine. Sheridan Lea concluded 

 that urease was soluble in water after the cells had been killed 

 by alcohol, but that otherwise it was intracellular. It can 

 hardly be said that Sheridan Lea's experiments are quite 

 convincing ; the writer has endeavoured to repeat them with 

 ordinary urine, so far with little success. The existence of 

 urease, apart from the organism, whether the latter is in a 

 living state or in the form of its dead cells, is not, in the writer's 

 opinion, as yet fully established, and it is possible, therefore, 

 that the cell substance itself may not be without effect upon 

 the reaction. Be this as it may, the essential fact remains 

 that the nitrogen of albuminoid material appears in the course 

 of the digestive process of animals, and of the putrefactive 

 changes taking place in nature, in the form of amino acids 

 or urea, which are apparently not available for plant food 

 until they have undergone the ammoniacal fermentation which 

 has just been described. Nitrogen in the form of carbonate 

 of ammonia is capable of serving as plant food ; in the plant 

 it is built up again into vegetable albumins which form the 

 food of animals. 



