20 QUARTERLYJOURNAL. 



is necessary to surround the roots with manures containing an 

 additional amount of nitrogen. 



Let us now see what are sources whence the ammonia is deriv- 

 ed for the use of plants. 



The flesh of animals, and a large portion of the blood, consists 

 of nitrogenized principles, fibrin, albumen, gelatine, which dur- 

 ing its decomposition after death, gives off the nitrogen in the form 

 of carbonate of ammonia. 



During life, the animal tissues are continually undergoing a 

 change, receiving new matter from the products of digestion, and 

 giving up their old materials which are thrown ofFin the excretions 

 from the lungs and kidneys. By the former, (the lungs,) is thrown 

 off the carbon, in the shape of carbonic acid, and by the latter, 

 (the kidneys,) the nitrogen in the shape of urea, which by expo- 

 sure to the atmosphere, is speedily converted into carbonate of 

 ammonia. 



Thus it is that all the nitrogen which enters into the foorl of ani- 

 mals, and which is directly or indirectly furnished by plants, after 

 making part of the living tissue of the animals, is ultimately re- 

 stored to the atmosphere in the shape of ammonia, or its carbo- 

 nate. 



Just as animals consume the carbon of vegetables, and after- 

 wards restore it to the atmosphere in the shape of carbonic acid, 

 that is in a shape adapted for vegetable nourishment, so do animals 

 restore the nitrogen they consume in their food to the atmosphere, 

 in the shape of carbonate of ammonia, which again serves for the 

 nourishment of vegetables. 



The ammonia or carbonate of ammonia, which is thus disengag- 

 ed from animals after death, and from their excretions during life, 

 being volatile, passes into the atmosphere. By reason of its affi- 

 nity for water, it combines with the vapor of the air, and descends 

 to the earth in the form of rain or snow, and is applied to the 

 roots of plants. Ammonia never exists in the atmosphere in suf- 

 ficient quantity to be detected by chemical analysis, but its pre- 

 sence in rain and snow water, proves that it must have previously 

 existed in the atmosphere. 



Plants, also, can absorb ammonia directly from the atmosphere 

 by means of their leaves. This seems to be proved by the expe- 

 riments of Boussaingault, to which I have before alluded. He 



