332 THE FERMENTATION OF UKEA. 



dioxide on the one hand and ammonia on the other, i.e. two 

 compounds which are known to be suitable for the nutrition of 

 plants and may be regarded as a condensation product from these 

 two atomic groups by dehydration. If their coherence can be 

 loosened, and the carbamide split up by hydrolysis to form carbon 

 dioxide and ammonia 



CO{NH 2 ) 2 + 2H 2 O = C0 2 + (NH 4 ) 2 O, 



this prevents the danger of the said quantity of urea remaining 

 undecomposed and accumulating, in consequence of which its 

 nitrogen would be withheld from, instead of restored to, the 

 vegetable kingdom. 



There is, however, no need to seek far for an instrument for 

 this conversion, Nature herself having already provided the imple- 

 ments for this Avork in the micro-organisms known as urea bacteria. 

 The next three paragraphs will be devoted to the consideration of 

 their character and capabilities ; a fourth dealing with the decom- 

 position of uric acid and hippuric acid. 



187. Discovery of the Urea-Ferment by Pasteur. 



The natural process of the decomposition of urea was discovered 

 some two years after the first successful attempt at the artificial 

 preparation of this substance. The well-known fact that urine, 

 which is clear when first voided by healthy individuals, be- 

 comes turbid on prolonged standing, while with increasing age it 

 turns more and more alkaline, and exhibits an increasing smell 

 of ammonia, found an explanation in 1830 at the hands of Dumas, 

 who regarded this modification (the ammoniacal fermentation of 

 urine) as a conversion of urea 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 incorrect- 

 ness of this view. He discovered in fermented urine a micro- 

 coccus (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 TIEGHEM (VIII.), and called 

 Bacterium urece, being subsequently named by Cohn Micrococcus 

 urece. 



The next researches on this important fermentation appeared 

 in 1879, an( i 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 com- 

 petitors, 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. 



