This state of things had a double effect. Food is the result of two essential ingredients--land and labor. The diminution in the amount of labor applied to the soil, consequent upon the removal of the laborers from the land, lessened the quantity of food; while the consumption of that food in cities and towns, and the waste of the fertile ingredients which should be restored to the soil, tended to exhaust the land, and led to vast importations of foreign and the manufacture of mineral manures. I shall not detain you by a discussion of this aspect of the question, which is of very great moment, consequent upon the removal of large numbers of people from rural to urban districts; but I may be excused in saying that agricultural chemistry shows that the soil--"perpetual man"--contains the ingredients needful to support human life, and feeding those animals meant for man's use. These ingredients are seized upon by the roots of plants and converted into aliment. If they are consumed where grown, and the refuse restored to the soil, its fertility is preserved; nay, more, the effect of tillage is to increase its productive power. It is impossible to exhaust land, no matter how heavy the crops that are grown, if the produce is, after consumption, restored to the soil. I have shown you how, in the reign of Queen Elizabeth, a man was not allowed to sell meat off his land unless he brought to, and consumed on it, the same weight of other meat. This was true agricultural and chemical economy. But when the people were removed from country to town, when the produce grown in the former was consumed in the latter, and the refuse which contained the elements of fertility was not restored to the soil, but swept away by the river, a process of exhaustion took place, which has been met in degree by the use of imported and artificial manures. The sewage question is taken up mainly with reference to the health of towns, but it deserves consideration in another aspect--its influence upon the production of food in the nation. An exhaustive process upon the fertility of the globe has been set on foot. The accumulations of vegetable mould in the primeval forests have been converted into grain, and sent to England, leaving permanent barrenness in what should be prolific plains; and the deposits of the Chincha and Ichaboe Islands have been imported in myriads of tons, to replace in our own land the resources of which it is bereft by the civic consumption of rural produce.