FORM IN WHICH AMMONIA IS PRESENTED. 49 



ulso subject to the influence of the direct rays of the sun ; an 

 nfluence necessary to effect the disengagement within their stem 

 and leaves of the oxygen which shall unite with the ammonia to 

 form nitric acid. 



The urine of men and of carnivorous animals contains the 

 largest quantity of nitrogen, partly in the form of phosphates, 

 partly as urea. Urea is converted during putrefaction into car- 

 bonate of ammonia, that is to say, it takes the form of the very 

 salt in rain-water. Human urine is the most powerful manure 

 for vegetables rich in nitrogen ; the urine of cattle, sheep, and 

 horses, contains less nitrogen ; but yet far more than the solid 

 excrements of these animals. In addition to urea, the urine of 

 herbivorous animals contains hippuric acid, which is decomposed 

 during putrefaction into benzoic acid, and ammonia. The latter 

 causes the formation of gluten, but the benzoic acid often remains 

 unchanged : for example, in the Anthoxanihum odoratum. 



The solid excrements of men and of animals contain compara- 

 tively very little nitrogen, but this could not be otherwise. The 

 food taken by animals supports them only in so far as it offers to 

 the various organs elements for assimilation which they may 

 require for their increase or renewal. Corn, grass, hay, and all 

 plants, without exception, whether fresh or dried, contain highly 

 azotised substances. The quantity of food required by animals 

 for their nourishment diminishes or increases in the same propor- 

 tion as it contains more or less of the substances containing 

 nitrogen. A horse may be kept alive by feeding it with 

 potatoes, a food containing a very small quantity of nitrogen ; 

 but life thus supported is a gradual starvation ; the animal 

 increases neither in size nor strength, and sinks under every 

 exertion. The quantity of rice consumed by an Indian astonishes 

 the European ; but the fact that rice contains less nitrogen than 

 any other kind of grain at once explains the circumstance. 



Now, as it is evident that the nitrogen of the plants and seeds 

 used by animals as food must be employed in the process of 

 assimilation, it is natural to expect that the solid excrements of 

 these animals will be deprived of it in proportion to the perfect 

 digestion of the food, and can only contain it when mixed with 

 secretions from the liver and intestines. Under all rireumstan. 

 4 



