therefore, that Seius[22] bought a white nightingale, as a present for the empress Agrippina, at the price of six thousand sestertii, equal to about fifty pounds of our present money; and that Asinius Celer[23] purchased a surmullet at the price of eight thousand sestertii, equal to about sixty-six pounds thirteen shillings and fourpence of our present money; the extravagance of those prices, how much soever it may surprise us, is apt, notwithstanding, to appear to us about one third less than it really was. Their real price, the quantity of labour and subsistence which was given away for them, was about one-third more than their nominal price is apt to express to us in the present times. Seius gave for the nightingale the command of a quantity or labour and subsistence, equal to what L.66 : 13 : 4d. would purchase in the present times; and Asinius Celer gave for a surmullet the command of a quantity equal to what L.88 : 17 : 9d. would purchase. What occasioned the extravagance of those high prices was, not so much the abundance of silver, as the abundance of labour and subsistence, of which those Romans had the disposal, beyond what was necessary for their own use. The quantity of silver, of which they had the disposal, was a good deal less than what the command of the same quantity of labour and subsistence would have procured to them in the present times. _Second sort._--The second sort of rude produce, of which the price rises in the progress of improvement, is that which human industry can multiply in proportion to the demand. It consists in those useful plants and animals, which, in uncultivated countries, nature produces with such profuse abundance, that they are of little or no value, and which, as cultivation advances, are therefore forced to give place to some more profitable produce. During a long period in the progress of improvement, the quantity of these is continually diminishing, while, at the same time, the demand for them is continually increasing. Their real value, therefore, the real quantity of labour which they will purchase or command, gradually rises, till at last it gets so high as to render them as profitable a produce as any thing else which human industry can raise upon the most fertile and best cultivated land. When it has got so high, it cannot well go higher. If it did, more land and more industry would soon be employed to increase their quantity.