KKSKAKCIIKS OF P. MigrKL 255 



into ammonium carbonate by the absorption of water. This hydrolysis of urea 

 was considered as a purely chemical process, a readjustment of the atoms in the 

 molecule. 



It was reserved for PASTEUR (I.) in 1862 to show the incorrectness of this 

 view. He discovered in fermented urine a micrococcus (0.8-1.0 p. in diameter, 

 and frequently united as diplococci, tetrads, and chains) which is capable of 

 inducing the change in question in sterilised urine. This organism was shortly 

 afterwards (in 1864) also described by VAN TIECIIKM (VIII.), :m<l called 

 Bacterium urece, being subsequently named by Cohn Micrococcus urc, . 



The next researches on this important fermentation appeared in 1879, and 

 afforded proof that this capacity for converting urea into ammonium carbonate 

 is not restricted to one single species of microbe, but that, on the contrary, 

 Pasteur's micrococcus has competitors, not only in many bacteria, but also in a 

 few of the higher fungi. This work was performed by P. MIQUEL (V.), to 

 whom we owe most of our present knowledge of the fermentation of urea. 

 Before turning to his more recent labours on the subject, we will, however, 

 briefly review the endeavours made by his colleagues in the same direction. 



R. VON JAKSCH (I.) in 1881 published a thoroughgoing investigation, the 

 morphological part of which was also instrumental in founding the theory of 

 bacterial pleomorphism ; the physiological results will be given in the next 

 paragraph. The urine-bacterium discovered by him throve best in a liquid 

 containing the following dissolved salts per litre of water : acid potassium 

 phosphate, 0.12 gram ; magnesium sulphate, 0.06 gram ; Seignette salt, 5 grams; 

 and urea, 3 grams. This liquid is known in the literature of the subject as 

 Jaksch's nutrient solution. 



LEUBE (I.) in 1885 added four new species of bacteria to the group of urea 

 ferments already known. One of them, called Bacterium urece, appeared in the 

 form of plump rods, 2 p, long and i \i broad, and of the remaining three, one 

 belongs to the sarcina group. 



In contrast to the bacteria (forming solid colonies) mentioned above is the 

 urea-fermenting micrococcus discovered by FLUGGE (1.), and known from its 

 liquefying influence on gelatin as Micrococcus urecv liquefctciens. 



The report drawn up by 0. LUNDSTROM (I.) and R. OAMBIER (I.) also made 

 known a few new species of urea-fermenting bacteria, and the same applies to a 

 research by R. BURRI, E. HERFELDT, and A. STUTZER (I.), which we will deal 

 with briefly below. We can now turn our attention to the above-mentioned 

 newer 



188. Researches of P. Miquel (VI.). 



This author isolated from air, soil, liquid manure, water, &c., some sixty 

 different species of bacteria, all of them capable of fermenting urea. Out of 

 these he selected seventeen as particularly worthy of interest, and has more 

 closely investigated and described them. Morphologically he distinguishes three 

 genera, Urobacillus, Urococcus, Urosarcina. In the further subdivision within 

 these three groups two principal factors of a chemico-physiological nature are 

 adopted as criteria, viz., the rapidity of fermentation, i.e. the amount of urea 

 fermented per unit of time ; and on the other hand, the fermentative power, 

 expressed by the maximum quantity of urea completely fermented by the 

 species in question per unit volume of nutrient solution. These two indications 

 acquire almost the character of mathematical constants for any determined 

 species. 



The most powerful as well as the most energetic is the Urobacillus Past' 

 so frequent in both natural and drainage waters. This organism ferments 

 3 grams of urea per hour in a 2 per cent, peptonised urea -bouillon, and 



