This information was obtained by an admirable regulation, which has scarcely a counterpart in the annals of a semi-civilized people. A register was kept of all the births and deaths throughout the country, and exact returns of the actual population were made to government every year, by means of the quipus, a curious invention, which will be explained hereafter.25 At certain intervals, also, a general survey of the country was made, exhibiting a complete view of the character of the soil, its fertility, the nature of its products, both agricultural and mineral,- -in short, of all that constituted the physical resources of the empire.26 Furnished with these statistical details, it was easy for the government, after determining the amount of requisitions, to distribute the work among the respective provinces best qualified to execute it. The task of apportioning the labor was assigned to the local authorities, and great care was taken that it should be done in such a manner, that, while the most competent hands were selected, it should not fall disproportionately heavy on any.27 The different provinces of the country furnished persons peculiarly suited to different employments, which, as we shall see hereafter, usually descended from father to son. Thus, one district supplied those most skilled in working the mines, another the most curious workers in metals, or in wood, and so on.28 The artisan was provided by government with the materials; and no one was required to give more than a stipulated portion of his time to the public service. He was then succeeded by another for the like term; and it should be observed, that all who were engaged in the employment of the government--and the remark applies equally to agricultural labor--were maintained, for the time, at the public expense.29 By this constant rotation of labor, it was intended that no one should be overburdened, and that each man should have time to provide for the demands of his own household. It was impossible--in the judgment of a high Spanish authority--to improve on the system of distribution, so carefully was it accommodated to the condition and comfort of the artisan.30 The security of the working classes seems to have been ever kept in view in the regulations of the government; and these were so discreetly arranged, that the most wearing and unwholesome labors, as those of the mines, occasioned no detriment to the health of the laborer; a striking contrast to his subsequent condition under the Spanish rule.31