334 THE FERMENTATION OF UREA. 



Morphologically similar to this, but differing greatly in physio- 

 logical character, is the Urobacillus Freudenreiehii, found with 

 particular frequency in the sweepings of the streets of Paris. This 

 bacillus can only hydrolise 0.3 gram of urea per hour, and cannot 

 ferment a larger quantity than 45 grams per litre of nutrient 

 solution. It is an actively motile rod, 1.0-1.3 /* broad and of 

 variable length. 



High degrees of speed and power of fermentation are not 

 always found in association. This is well exemplified by Uro- 

 bacillus Schutzenberyii, a rod i /x long and 0.5 ju, broad, incapable 

 of producing spores. It was found by Miquel both in natural 

 and drainage waters, but never in the air. This species is very 

 energetic, i.e. transforms a large amount of urea per unit of time, 

 but its activity ceases as soon as the liquid has become somewhat 

 enriched with ammonium carbonate. That this is actually the 

 cause of the cessation follows from the fact that the fermentation 

 proceeds further when this salt is removed by aerating the 

 medium. 



To this injurious influence of ammonium carbonate towards 

 which different degrees of susceptibility are exhibited by the 

 various species is due the rapid dying of cultures of the bacteria 

 under consideration, in liquids containing urea. If it is desired 

 to prolong their existence or to refresh debilitated cultures, they 

 must be transferred to nutrient media that are free from urea, 

 and consequently enable growth to proceed only at a slow rate, 

 but, just for this reason, ensure a longer life. 



Even greater than their sensitiveness towards ammonium car- 

 bonate, of which even the most delicate species can support a 

 very considerable quantity, is the susceptibility of the urea bacteria 

 to the presence of free acid in the nutrient medium. Burri and 

 his collaborators ascertained (in their above-mentioned researches) 

 that 0.4 per cent, of sulphuric acid produces a fatal effect. This 

 observation can be practically utilised in the protection of stall 

 manure from early decomposition. 



Into the remaining distinguishing characteristics of Miquel's 

 urobacteria especially the degree of resistance to heat exhibited 

 both by the vegetative forms and the spores produced by all but 

 the last-named species we cannot enter further. One common 

 characteristic peculiar to the group must not, however, be omitted 

 from mention, and that is the aureole with which the colonies 

 surround themselves when grown on 2 per cent, urea-gelatin, and 

 whereby they are distinguishable from all other bacterial species, 

 even at an early age, by macroscopical examination or under a low 

 power. The colonies are closely surrounded, for a distance ex- 

 ceeding their diameter, with numerous biscuit-shaped bodies, 

 embedded in the gelatin and for the most part so close together 

 that they envelop the colony as in a cloud. These bodies are 

 facetted crystals, each composed of two combined globules, con- 



