475 



carbonic acid, until the plant rises above the ground, and the leaves 

 and other portions of its organism are formed, to enable it to gather, in 

 the form of carbonic acid, its food from the air. Its organic constitu- 

 ents must be found in the soil or in the manure in the form of silicates, 

 carbonates, or phosphates, and may be supplied in a crude form as in 

 potash, ashes, lime, bones, &c. Its nitrogen is to be supplied, in the 

 form of ammonia, from decayed animal or vegetable substances in one 

 way or another. The excrements of some animals are in this respect 

 much richer than those of others. The excrements of man are much 

 richer in nitrogen, than those of any other animals, and those of men 

 living upon animal more so than those of men living upon vegetable 

 diet. In the urine of animals nitrogen is found in much greater abun- 

 dance than in the solid excrements. In respect to nitrogen, 100 parts 

 of the urine of a healthy man are equal to 1300 parts of the fresh dung 

 of a horse. This ammonia is supplied in the soil ; or floating in the 

 air, it is taken up by rain water or by snow, and supplied to the vege- 

 tation in that form. The manures of different animals likewise return 

 to the soil the inorganic constituents of plants, the various salts which 

 have formed a part of the vegetable products, which have been taken 

 from the fields and been consumed by the cattle ; and thus every thing 

 goes on in an eternal round of reciprocity. 



I have thus given a general and imperfect sketch of the main princi- 

 ples of the work of Liebig. I have confined myself to the part, which 

 is principally agricultural. The second part, on chemical transforma- 

 tions, fermentation, putrifaction, decay, and various kindred subjects, 

 is equally interesting. The work of Liebig displays extraordinary phi- 

 losophical acumen, and confers upon him the highest honor. The 

 more it is examined, the deeper will be the interest which it will create, 

 and the stronger the admiration of the ability with which it is written. 

 It is not a work to be merely read, but studied ; and if further inquiries 

 and experiments should demonstrate, as seems to us from many facts 

 within our own knowledge in the highest degree probable, the sound- 

 ness of his views, his work, not merely as a matter of interesting 

 philosophical inquiry, but of the highest practical utility, will be inval- 

 uable. 



There are various notes, appended to the volume, of great interest. 

 A long and highly interesting note is appended, containing some letters 

 from Dr. S. L. Dana, of Lowell, to Dr. Hitchcock, of Amherst Col- 

 lege, and taken from the forthcoming third edition of Dr. Hitchcock's 



