RESEARCHES OF P. MIQUEL. 335 



taining lime, carbonic acid, and phosphoric acid, and formed by 

 the reaction of ammonium carbonate (liberated by the bacteria), 

 on the salts of the alkaline earths contained in the medium. 



Whether and how far the nitrogen in the urea contributes to 

 the structure of these bacteria is also an interesting point. Jaksch 

 in his treatise asserted that his bacillus preferentially takes up 

 nitrogen from urea, other sources, such as peptone, being less 

 suitable ; but Miquel came to exactly the opposite conclusion, the 

 species examined by him greatly preferring peptone, or any similar 

 substance, before urea as a source of nitrogen. 



Urobacteria are of very frequent occurrence in nature. For 

 quantitative determinations on this point we are indebted to 

 Miquel, according to whom the average number of such bacteria 

 in the air of Paris was (in 1891) 151 germs per cubic metre. The 

 smallest number (90) was found in autumn and the highest in 

 spring (197) and summer (202). The relative content of these in 

 natural waters increases with the degree of impurity. A good 

 example is afforded Iby the Seine: before reaching Paris 103 

 urobacteria were found per 10,000 microbes, whereas a sample 

 taken within the city limits gave 204, or twice as many as before. 

 According to Miquel, 1-2 per cent, of the bacteria present in the 

 soil, and 15 per cent, of those in cowhouse manure, are capable of 

 hydrolysing urea. It is therefore evident that Nature provides 

 for the conversion of urea into a more readily assimilable compound, 

 which we have already found to be essential. 



The ammoniacal fermentation of the urine of herbivorous 

 domestic animals (horses, horned cattle) begins soon after its 

 evacuation from the body. The resulting ammonium carbonate 

 partly volatilises, and thereby leads to a loss of nitrogen, the extent 

 of which as A. MUNTZ and A. GIRARD (I.) showed in 1893 was 

 formerly under-estimated. Out of the many methods proposed 

 and attempted for the prevention of this loss and the combination 

 of the ammonia, a few (e.g. sulphuric acid) have proved unfit for 

 application in the stall, and others (such as peat litter, gypsum, 

 kainit) insufficient, only a single one being actually suitable : the 

 superphosphate recommended by E. HEIDEN (I.) in 1887, viz., the 

 acid phosphate prepared by means of sulphuric acid, and capable 

 not only of chemically fixing ammonia, but also, by reason of its 

 acid reaction, preventing the inception of uric fermentation. 



189. Urase. 



In 1874 MUSCULUS (I.) expressed the opinion that the con- 

 version of urea into ammonium carbonate is merely an indirect 

 result of bacterial activity, the hydrolysis of the urea being 

 effected not by the organisms themselves, but by the enzyme they 

 excrete. This enzyme was said to be particularly plentiful in, 

 and recoverable from, the urine of patients suffering from catarrh 



