254 THi: FERMENTATION OF URKA 



cent., in horses' urine up to 2 per cent, (in combination with lime). Urea 

 is present to the extent of 2-5 per cent, in cows' urine, and 3 per cent, in that 

 of the hors-e. 



186. Urea Unassimilable by Higher Plants. 



uming the total number of inhabitants in the world to be 1500 millions, 

 and intimating the diurnal excretion of urea at an average of only 25 grams per 

 individual, then there results a total daily production of 37,500 tons of urea by 

 the human race alone. This quantity in the solid state would occupy a space of 

 50,000 cubic metres (65,400 cubic yards), and contain 17,000 tons of combined 

 nitrogen. The excretions of the animal kingdom must be estimated at a much 

 higher figure. 



The amount of nitrogen daily excreted in urine and passing into manure is 

 consequently enormous, and the question naturally arises : What becomes of it 

 afterwards * Js urea (and also uric acid, etc.) adapted to serve immediately and 

 directly for the nutrition of plants, and of cultivated plants in particular? 



Agricultural practice answers this query by a decided negative, knowing 

 from experience that manuring with fresh urine is at first either entirely useless 

 or actually injurious. No satisfactory explanation of this fact lias yet been 

 discovered by scientific research. O. KELLNER (III.), for example, sought it in 

 the circumstance that urea is not absorbed (retained) by the soil. We must 

 therefore turn away from research, and fall back on the fact that urea is 

 unsuitable for the nutrition of the higher plants ; and that consequently its 

 nitrogen, not being available for this purpose, is lost. If this element is to 

 continue its cycle in the organic world, it must first be converted into other 

 forms and modes of combination ; and the question arises as to which of these 

 involves the least labour and smallest expenditure of energy. 



It must be borne in mind that urea is a derivative of carbon dioxide 011 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 = C0 2 + (NH 4 ) 2 0, 



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 implements for this work 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 decomposition 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 

 sub>tance. The well-known fact that urine, which is clear when first voided by 

 healthy individuals, becomes 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 



