RESEARCHES OF P. MIQUEL. 333 



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 investi- 

 gation, 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, o. 1 2 

 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 //, 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 (I.), 

 and known from its liquefying influence on gelatin as Micrococcus 

 urece liquefaciens. 



The report drawn up by C. LUNDSTROM (I.) and R. CAMBIER (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 fer- 

 menting 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, Urobacillua, 

 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 

 Urdbaeillus Pasteurii, 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 completes its task even 

 when the nutrient solution contains 140 grams of urea per litre. 



