The Wealth of Nations by Part 1 Chapter 8 Page 54

reason and humanity, they have frequently occasion rather to moderate than to animate the application of many of their workmen. It will be found, I believe, in every sort of trade, that the man who works so moderately as to be able to work constantly not only preserves his health the longest, but, in the course of the year, executes the greatest quantity of work.

In cheap years, it is pretended, workmen are generally more idle, and in dear ones more industrious than ordinary. A plentiful subsistence, therefore, it has been concluded, relaxes, and a scanty one quickens their industry. That a little more plenty than ordinary may render some workmen idle, cannot well be doubted; but that it should have this effect upon the greater part, or that men in general should work better when they are ill fed than when they are well