OF THE NITROGEN OF PLANTS. 83 



The urine of men and of carnivorous animals 

 contains a large quantity of nitrogen, partly in the 

 form of phosphates, partly as urea. Urea is con- 

 verted during putrefaction into carbonate of am- 

 monia,, that is to say, it takes the form of the very 

 salt which occurs in rain-water. Human urine is 

 the most powerful manure for all vegetables con- 

 taining nitrogen ; that of horses and horned cattle 

 contains less of this element, but infinitely 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 enters into the composition of the gluten, but 

 the benzoic acid often remains unchanged : for 

 example, in the Anthoxanthum odoratum. 



The solid excrements of animals contain compa- 

 ratively very little nitrogen, but this could not be 

 otherwise. The food taken by animals supports 

 them only in so far as it offers elements for assimi- 

 lation to the various organs, which they may require 

 for their increase or renewal. Corn, grass, and 

 all plants, without exception, contain azotised 

 substances. The quantity of food, which animals 

 take for their nourishment, diminishes or increases 

 in the same proportion, as it contains more or less 

 of the substances containing nitrogen. A horse may 

 be kept alive by feeding it with potatoes, which 

 contain a very small quantity of nitrogen ; but life 

 thus supported is a gradual starvation ; the animal 



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