FIRST REPLY. 151 



per acre, which contain about l,600lbs. of carbon. But 

 we do not manure the soil of the forests, and its supply 

 of humus, far from being exhausted, increases considerably 

 from year to year, from the breakage by wind and from 

 the fall of the leaf. The hay-maker of Switzerland and 

 Tyrol mows his definite amount of grass every year on the 

 Alps, inaccessible to cattle, and gives not back the smallest 

 quantity of organic substance to the soil. Whence comes 

 this hay, if not from the atmosphere ? The plant requires 

 carbon and nitrogen, and in South America, in the woods 

 and on the wild Alps, there is no possibility of its acquiring 

 these matters except from the ammonia and carbonic acid 

 of the atmosphere. The northern provinces of Holland, 

 Friesland, Groningen and Drenthe, export annually about 

 a million pounds of nitrogen in their cheese. They obtain 

 it through the cows from their meadows, which receive 

 no manure but that from the cattle grazing thereon. The 

 meadows receive no return by this, since all that the cows 

 produce comes itself from the meadows. Whence then 

 these enormous quantities of nitrogen ? Perhaps Vesuvius 

 or Etna, or the great fire-abysses of the Cordilleras pour 

 forth this abundance of carbonate of ammonia, which is 

 carried by currents of air to the plants of the Dutch mea- 

 dows, and then, through the cows, becomes as caseine, an 

 object of trade and of delight to the palate. 



These and innumerable similar facts, taken together, 

 give us a very safe conclusion, which has finally been placed 

 beyond doubt by the experiments of Boussingault, the most 

 extensive and almost the only really scientific researches 

 which have been instituted in agricultural inquiries. Bous- 

 singault devoted, on his estate at Bechelbronn, in Alsace, 

 four hectares of land (nearly five acres) to experiments 

 which were pursued with undeviating accuracy for many 



