216 BACTEEIOLOGICAL AND ENZYME CHEMISTRY 



The ammoniaoal fermentation belongs to an increasing 



number of such changes, which can ultimately be referred to 



the activity of a non-hving 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 alcohoHc 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 httle 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 fuUy estabhshed, 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. 



