Although the examples of this last extremity are not common in some countries, yet I believe they are more so than is generally imagined; and the other stages of want are productive of many diseases, and of a decay which extinguishes the faculty of generation, or which weakens it, so as to produce children less vigorous and less healthy. I appeal to experience, if this reasoning be not just. Put two or three pairs of rabbits into a field proper for them, the multiplication will be rapid; and in a few years the warren will be stocked: you may take yearly from it a hundred pairs, I shall suppose, and keep your warren in good order: give over taking any for some years, you will perhaps find your original stock rather diminished than increased, for the reasons above mentioned. Africa yearly furnishes many thousands for the cultivation of America; in this she resembles the warren. I have little doubt but that if all her sons were returned to her, by far the greater part would die of hunger. ------------------------------------------------------------------------ CHAP. IV. _Continuation of the same Subject, with regard to the natural and immediate effects of Agriculture, as to Population._ I proceed in my examination. I now suppose man to add his labour and industry to the natural activity of the soil: in so far, as by this he produces an additional quantity of food, in so far he lays a foundation for the maintenance of an additional number. This number I shall call (B). From this I conclude, that as (A) is in a constant proportion to the spontaneous fruits, so (B) must be in proportion to agriculture (by this term I understand at present every method of augmenting food by labour) consequently the number maintained by the labour of mankind must be to the whole number of mankind as (B) is to (A + B), or as (B) is to (A) and (B) jointly. By this operation we find mankind immediately divided into two classes; those who, without working, live upon the spontaneous fruits of the earth; that is, upon milk, cattle, hunting, &c. The other part, those who are obliged to labour the soil. It is proper next to inquire what should naturally oblige a man to labour; and what are the natural consequences of it as to multiplication.