We have, nevertheless, a means of restoring to fertility many of our worn-out lands, and preserving our fertile fields from so rapid impoverishment as they are now suffering. Many suppose that soils which produce good crops, year after year, are inexhaustible, but time will prove to the contrary. They may possess a sufficiently large stock of phosphoric acid, and other constituents of plants, to last a long time, but when that stock becomes so reduced, that there is not enough left for the uses of full crops, the productive power of the soil will yearly decrease, until it becomes worthless. It may last a long time, a century, or even more, but as long as the system is--to _remove every thing, and return nothing_,--the fate of the most fertile soil is evident. The source mentioned, from which to obtain phosphoric acid, is the bones of animals. These contain large quantities of _phosphate of lime_. They are the receptacles which collect nearly all of the phosphates in crops, which are fed to animals, and are not returned in their excrements. For the grain, etc., sent out of the country, there is no way to be repaid except by the importation of this material; but, all that is fed to animals, or to human beings, may, if a proper use be made of their excrement, and of their bones after death, be returned to the soil. With the treatment of animal excrements we are already familiar, and we will now turn our attention to the subject of BONES. [Of what do dried bones consist? What is the organic matter of bones? The inorganic? What can you say of the use of whole bones?] _Bones_ consist, when dried, of about one third organic matter, and two thirds inorganic matter. The organic matter consists chiefly of _gelatine_--a compound containing _nitrogen_. The inorganic part is chiefly _phosphate of lime_. Hence, we see that bones are excellent, as both organic and mineral manure. The organic part, containing nitrogen, forms _ammonia_, and the inorganic part supplies the much needed _phosphoric acid_ to the soil. Liebig says that, as a producer of ammonia, 100 lbs. of dry bones are equivalent to 250 lbs. of human urine. [How does the value of bone dust compare with that of broken bones? What is the reason of the superiority of bone dust? How is bone-black made? Of what does it consist?] Bones are applied to the soil in almost every conceivable form. _Whole bones_ are often used in very large quantities; their action, however, is extremely slow, and it is never advisable to use bones in this form. Ten bushels of bones, finely ground, will produce larger results, during the current ten years after application, than would ensue from the use of one hundred bushels merely broken, not because the dust contains more fertilizing matter than the whole bones, but because that which it does contain is in a much more available condition. It ferments readily, and produces ammonia, while the ashy parts are exposed to the action of roots.