ANIMALS AND THEIR PRODUCTS. 99 



pend crops on the farm, we return to the soil all we 

 took from it, and as much more as the growing plants 

 draw from the air, which is nearly all their organic 

 matter. In this way a farm should be constantly 

 gaining in fertility ; for on the supposition that we 

 sell nothing from the farm, we keep all the inorganic 

 parts of the soil at home, and by means of growing 

 plants we are all the while gathering inorganic matter 

 from the air and incorporating it with the soil ; so that 

 the soil, treated thus, would remain equally rich in 

 the inorganic (mineral) parts, and be growing every 

 year richer in the organic parts. It will be seen also, 

 that if we sell off crops, or anything that is made from 

 crops, as beef, pork, butter, cheese, the soil must be 

 from that time becoming poorer in the inorganic ingre- 

 dients, unless we procure fertilizers from off the farm 

 and substitute them for those which we send away ; 

 for when we sell any product of the farm, we sell a 

 part of the soil ; not enough in a single pound of but- 

 ter to diminish sensibly the quantity left, but enough 

 in a century, in all the butter that may be sold from 

 cows fed on a single pasture, to leave that pasture en- 

 tirely destitute of certain ingredients, without which 

 good butter cannot be made. So if the hay from a 

 mowing was to be sold off for many years and nothing 

 returned, certain ingredients of the soiWould become 

 so exhausted, that little or no more hay could be 

 grown on that soil ; or if the corn, wheat, or rye were 

 to be sold from a soil, the result would be the same. 

 If a soil were eminently good, it would resist bad 

 treatment a long time, but sooner or later it would be 

 exhausted. The farmer who should have sold all his 



