166 SELECTIONS FROM ADDRESSES 



table or animal food, he derives from it the very same princi- 

 ples, though not in the same proportion. Even the leaves of 

 most plants contain enough of nutriment to sustain life, espe- 

 cially in warm climates. But in their fruit, especially the dif- 

 ferent kinds of grain, it is more concentrated, and, in animal 

 food, still more so ; or rather such is the case with the nitrogen- 

 ized principles. Hence the question as to the use of animal 

 food, becomes reduced chiefly to one of experience, or conveni- 

 ence, or humanity. 



These theories of nutrition and animal heat cannot be re- 

 garded as completely established. But they are so much more 

 ingenious and satisfactory than any which have preceded them, 

 as to give them strong claims upon our attention. 



Geology teaches us that soil's are nothing but rocks crushed into 

 powder, and mixed up with vegetable or animal matter. Hence 

 we might expect that they would differ in composition as the rocks 

 differ; and so they do; though such has been the nature of the 

 agency by which the rocks were crumbled down, that the ma- 

 terials from several rocks are frequently mingled together. But 

 in fact, rocks do not differ very materially in composition. Some, 

 such as trap rock and limestone, contain more lime and magne- 

 sia than others. But there is scarcely any rock of much extent, 

 that does not contain all the earthy ingredients essential to 

 plants ; and, therefore, so far as their composition is concerned, 

 it is comparatively unimportant from what rock a soil is derived. 

 We shall be almost sure to find in it a large amount of silex, 

 more or less of alumina, lime, and magnesia, with gypsum and 

 phosphate of lime. Till within a few years, the latter substance, 

 so important to plants, was supposed to exist in a few soils only. 

 And it is to our countryman, Dr. S. L. Dana, that we are in- 

 debted for first suggesting that it could be found in all soils ; and 

 in accordance with this suggestion, in my examination of one hun- 

 dred and forty-six soils of Massachusetts, which I analyzed by 

 the direction of the Government, I found only one, and that, pure 

 sand, which did not contain phosphates. It was not until some 

 years after I had published these results, and the suggestion of 

 Dr. Dana, that any European chemist brought out the same idea ; 

 and therefore I claim for him the origination of this discovery, 

 which I consider a very important one in scientific agriculture. 



