URASE 257 



in spring (197) and summer (202). The relative content of these in natural 

 waters increases with the degree of impurity. A good example is afforded by 

 the Seine : before reaching Paris 103 urobacteria were found per 10,000 

 microbes, whereas a sample taken within the city limits gave 204, or twice as 

 many as before. According to Miquel, 1-2 per cent, of the bacteria present in 

 the soil, and 15 per cent, of those in cowhouse manure, are capable of hydrolys- 

 ing urea. It is therefore evident that Nature provides for the conversion of 

 urea into a more readily assimilable compound, which we have already found to 

 be essential. 



The ammoniacal fermentation of the urine of herbivorous domestic animals 

 (horses, horned cattle) begins soon after its evacuation from the body. The 

 resulting ammonium carbonate partly volatilises, and thereby leads to a loss 

 of nitrogen, the extent of which as A. MTJNTZ and A. GIRARD (I.) showed 

 in 1893 was formerly under-estimated. Out of the many methods proposed 

 and attempted for the prevention of this loss and the combination of the 

 ammonia, a few (e.g. sulphuric acid) have proved unfit for application in the 

 stall, and others (such as peat litter, gypsum, kainit) insufficient, only a single 

 one being actually suitable : the superphosphate recommended by E. HEIDEN (I.) 

 in 1887, viz., the acid phosphate prepared by means of sulphuric acid, and 

 capable not only of chemically fixing ammonia, but also, by reason of its acid 

 reaction, preventing the inception of uric fermentation. 



189. Urase. 



In 1874 Museums (I.) expressed the opinion that the conversion of urea into 

 ammonium carbonate is merely an indirect result of bacterial activity, the 

 hydrolysis of the urea being effected not by the organisms themselves, but by the 

 enzyme they excrete. This enzyme was said to be particularly plentiful in, and 

 recoverable from, the urine of patients suffering from catarrh of the bladder, a 

 circumstance which would also account for the alkaline reaction of this urine 

 when in a freshly voided condition. This statement was investigated and con- 

 firmed by PASTEUR and JOUBERT (II.) in 1876. On the other hand, the attempts 

 made by LEUBE (I.) to separate the enzyme from the bacteria by filtration 

 through a clay cylinder failed. P. MIQUEL (VII.) then showed, in 1890, that 

 these conflicting results are due to the extreme decomposability of this enzyme, 

 which he proposed to name urase, and which, being very easily oxidised, ought 

 to be filtered in an atmosphere devoid of oxygen, a precaution neglected by 

 Leube. Urase decomposes in three to four hours at 50 C., and in a very few 

 minutes at 80 C. With regard to its chemical composition nothing is at present 

 known ; not even whether it is a single body or a mixture of several substances 

 (varying in constitution according to the conditions of fermentation). One 

 thing, however, Miquel placed beyond doubt, viz., its capacity to hydrolyse and 

 rapidly convert urea (in a sterilised solution) into ammonium carbonate. It is 

 therefore a true enzyme. 



190. The Decomposition of Uric Acid and Hippuric Acid. 



With regard to the disruption of the uric acid molecule by microbial agency, 

 F. and L. SESTINI (I.) instituted an investigation, according to which the 

 decomposition corresponds to the equation- 



,NH C NH X NH 4 , 



II >C =0 + SH 2 + 30 = 4 >C0 3 + C0 2 



C-NH/ K' 



^NH C = 



