218 FARMYARD MANURE 



ammonium carbonate. A number of species form spores 

 which resist the temperature of a 95 to 100 C. for an 

 hour or more ; others do not produce spores, and are 

 easily destroyed by heating to 70 C. for a short time. 

 Some of them grow an ordinary beef gelatine media, 

 while others only develop on gelatine or agar media 

 containing urea. They differ very considerably in their 

 power of hydrolysing urea ; Urobacillus Pasteurii under 

 favourable conditions at 30 C. is able to decompose 

 3 gr. per litre per hour, while many of the Urococci are 

 only able to ferment this amount in twenty-four hours. 

 When grown on solid media containing urea a character- 

 istic whitish ring or halo appears, consisting of minute 

 powdery crystals of calcium carbonate mixed possibly 

 with calcium phosphate. 



The ammoniacal fermentation of urea by the uro- 

 bacteria is due to the action of an enzyme, urease, 

 which, according to Miquel is excreted into the sur- 

 rounding liquid nutrient medium in which the organisms 

 are cultivated. From such medium Miquel stated that 

 an active solution of urease can be obtained by filtra- 

 tion through a porcelain filter, but Beijerinck, Moll, 

 Leube, and others have not been able to confirm this. 

 Beijerinck has shown that in the passage of a liquid 

 culture of the uro-bacteria through filter paper many of 

 the organisms are kept back and the filtrate has little 

 fermentative action on urea, which would not be the case 

 if the urease was in solution. A precipitate can be 

 obtained by the addition of absolute alcohol to a ten to 

 fourteen days old culture, which when dried at 30 to 

 35 C. and added to a solution of urea sets up an ener- 

 getic ammoniacal fermentation at 48 to 50 C., specially 

 in the presence of small amounts of glycerine and 



