Such qualified labor, as is treated of here, may be most accurately estimated, the quality of which supposes a certain cost of acquisition. This cost may be considered as the outlay of so much capital, which, with interest,[167-7] should come back to the workman in his wages. Otherwise, others would be deterred from entering the same business by the example of his loss. Here, especially, it is necessary to take into account the long period of apprenticeship or tuition, and the large fees paid for the same; and this, whether they depend on the natural difficulties in the way of acquirement or on artificial obstacles opposed to freedom of competition.[167-8] The influence of these circumstances is particularly great in those kinds of labor which require a "liberal" education.[167-9] Among the costs of production proper, peculiar to this labor-force, must be included, also, the necessary support of the workman, during the interval between the completion of his studies and the beginning of his full reward.[167-10] When a species of work requires special current expenses to be made in order to its proper performance, these also should of course be made good to the workman in his wages. Most intellectual labor, for instance, requires quiet surroundings. The brain-worker cannot share his study with his family, and, therefore should receive wages or remuneration large enough in amount to enable him to arrange his dwelling accordingly. A similar circumstance, only in a much higher degree, enhances the price paid for diplomatic service. [Footnote 167-1: Excellent germs thereof in _Adam Smith_, Wealth of Nat., I, ch. 10, 1. Earlier yet, in _Galiani_, Della Moneta, I, 2. _Cantillon_, Nature du Commerce, 24 ff.] [Footnote 167-2: Even in the case of mere manual labor, for instance, a skillful packer of goods is paid higher wages than a mere day laborer; a sower better than a plowman or a digger; a vintner, in general, better than an agricultural laborer: in the Palatinate of the Rhine, in the ratio of 36:24. Thus, almost anyone can paint a door or a house, while an artist possesses a species of natural monopoly.] [Footnote 167-3: Thus, the Greek juggler, who understood how to throw lintels from a certain distance through the eye of a needle, was very appropriately rewarded by his king with a bushel of lintels. On the other hand, the high fee paid for an operation for cataract depends both on the great importance of the eye which cannot be replaced in any way, and on the rarity of the courage among doctors to pierce the eye of a living man. Very remarkable achievements, which it requires great education to understand, are generally paid for at a very low rate. (_Stein_, Lehrbuch, 123.)]