14 TRANSACTIONS. 



vegetables ; starch and sugar occur abundantly in many plants ; 

 and the fibrine, albumen and caseine, are derived from the 

 gluten of flour, the leguminous principle of beans, &.c. It 

 needs nothing, also, but water and the oxygen of the air, to 

 convert these various principles into one another ; and some- 

 times this can be done even by man. Thus, starch is easily 

 changed into sugar, and very palatable bread has been made 

 out of wood, which, in fact, is chiefly fibrine, and contains all 

 that is essential for nourishment. Who knows how soon it 

 may happen, that a few cords of wood shall furnish the poor 

 man not only with fuel, but with bread ? 



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 soils 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 t'le rocks d;fter : and so they do ; though such has been 

 the nature of the agency by which the rocks were crumbled 

 down, that the materials from several rocks are frequently 

 mingled together. But in fact, rocks do not diff'er very mate- 

 rially in composition. Some, such as trap rock and limestone, 

 contain more lime and magnesia than others. But there is 

 scarcely any rock of nmch extent, that does not contain all the 

 earthly ingredients essential to plants ; and, therefore, so far 

 as their composition is concerned, it is comparatively unimpor- 

 tant 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 alu- 

 mina, lime, and magnesia, with gypsum and phosphate of lime. 



But th 3 great ditferences in the fertility of soils depend more 

 upon the a.nount and condition of the organic matter which 

 they contain, and upon their power of absorbing and retaining 

 heat and moisture, and upon their degree of fineness or coarse- 

 ness, than upon their mineral constitution. Every farmer 

 knows that a soil may be too coarse or too fine for good crops, 

 and that it may be too cold ; and also that it may abound in 



