One would say that this apparent increase is due to the stimulating effect of the excreta upon the soil, which enables us to draw something extra from that inexhaustible storehouse of plant-food and water, and enables the animal to use these materials, instead of allowing them to drain to the springs, and so find their way to the sea. We know that a far greater proportion of the rainfall percolates through barren soil than through soil bearing crops. If this be so, there is a practical increase of the land at the expense of the water. Again, we must remember that our knowledge of the sources of the gases of the atmosphere is not complete. It may be that all the oxygen of the air is furnished by the green leaves of plants, and all the carbonic acid by processes of respiration and combustion, but we are by no means sure of this. Of the sources of the atmospheric nitrogen we know nothing. Now it is certain that much of the carbon of the atmosphere is appropriated by the plants, and much of the oxygen by the animals. If among the herbage there be plants of clover, it is now certain that much of the atmospheric nitrogen will be drawn into the soil to nourish these plants and generally to increase their fertility. Whether the return of oxygen, carbon, and nitrogen is, in the long run, equal to the intake we cannot tell. When, however, we ponder upon the gradual increase of vegetable soil or humus with which the bare rocks have been clothed in the course of ages, it is almost impossible not to come to the conclusion that the humus, and with it the fertility of the soil, has steadily increased at the expense of the sea on the one hand, and, possibly, of the atmosphere on the other. To put the matter in the form of question and in other terms, 'Does the _Lithosphere_ increase at the expense of the _Atmosphere_ and the _Hydrosphere_?' Does the land increase at the expense of sea and air? Be this as it may, it seems certain that by scrupulous return to the soil of all that comes out of it the resources of Nature are made increasingly available for the benefit of man. When organic matter is mixed with water, a process of putrefaction and fermentation is started, and the organic matter, instead of undergoing oxidation, is reduced, and among the commoner products of this process are ammonia with sulphuretted hydrogen and marsh-gas, which are both combustible. These processes furnish us with other combustible matters, among the commonest of which are the alcohols, the familiar products of fermentation.