154 MR, J. P. JOULE ON THE UTILIZATION OF THE 
tening animals, which are afterwards consumed by man. 
Another part is used directly in the form of potatoes, 
meal, or vegetables; while a third part, consisting of the 
remnants of plants, is employed as litter in the form of 
straw, &e. It is evident that all the constituents of the 
fields, removed from it in the form of animals, corn and 
fruit, may again be obtained in the liquid and solid excre- 
ments of man, and in the bones and blood of slaughtered 
animals. It altogether depends upon us to keep our fields 
in a constant state of composition and fertility by the 
careful collection of these substances. We are able to 
calculate how much of the ingredients of the soil are re- 
moved by a sheep, by an ox, or in the milk of a cow, or 
how much we couvey from it in a bushel of barley, wheat, 
or potatoes. From the known composition of tle excre- 
ments of man, we are also able to calculate how much of 
them it is necessary to supply to a field to compensate for 
the loss that it has sustained.” Again, in page 181, he 
says: “In the solid and liquid excrements of man and of 
animals; we restore to our fields the ashes of the plants 
which served to nourish these animals. These ashes con- 
sist of certain soluble salts and insoluble earths which a 
fertile soil must yield, for they are indispensable to the 
growth of cultivated plants. It cannot admit of a doubt 
that, by introducing these excrements to the soil, wesgive 
to it the power of affording food to a new crop, or, in other 
words, we reinstate the equilibrium which had been dis- 
turbed. Now that we know that the constituents of the 
food pass over into the urine and excrements of the animal 
fed upon it, we can with great ease determine the different 
value of various kinds of manure. The solid and liquid 
excrements of an animal are of the highest value, as manure 
Sor those plants which furnished food to the animal.” 
From the above incontestable principles we may easily 
calculate the magnitude of the loss which is sustained by 
