ON NITROGEN. 67 



united with the portion of carbon before no- 

 ticed, bat which need not here be farther 

 discussed. 



It appears to possess of itself a negative 

 effect on the animal frame ; its only use being 

 apparently to dilute the oxygen: but in the 

 vegetable economy its functions are far more 

 important, as it enters into combination with 

 many other substances composing the struc- 

 ture, and is itself assimilated, and constitutes 

 the most nutritious part of plants. 



It differs, however, materially from carbon, 

 the subject of the last section, in this respect, 

 that it is never absorbed by the leaves, or the 

 green parts of plants ; its only access is by the 

 roots in a fluid state : and this, therefore, will 

 simplify materially the consideration of this 

 substance. 



It is to the presence of this gas, assimilated 

 and combined, in the farina of wheat, oats, 

 barley, &c., as well as in the flesh of animals, 

 that the nutritive qualities of these substances 

 are to be attributed, and in proportioK as this 

 gaseous body is present in each case so is the 

 nourishment the food contains. 



The form in which nitrogen generally pre- 

 sents itself to our senses is in combination 

 with hydrogen, (one volume of the former 

 combining with three volumes of the latter) 

 and in this state it is known as ammonia; this 

 substance again combines with carbonic acid 

 gas, and forms carbonate of ammonia, one of 

 the most universally diffused substances in 



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