Mises.org amazes me by their offering of great economics texts on-line.  I read Satan’s Bushel over the course of two evenings, and I’m currently enjoying The New Deal in Old Rome.  I laughed out loud at the following quote from page 82 of The New Deal in Old Rome: “The coinage of money was a comparatively new invention for Rome. A
half-century before the final unification of Italy the capital had
reached a stage in its economic development when it no longer could do
business with the primitive coinage of which the unit was a chunk of
bronze weighing a pound.  As someone has said, with this money a
housewife’s journey to market must have been as fatiguing as her return.”

In Human Action, Mises says (page 410 of the third edition): “The regression theorem complies with this requirement.  It traces the specific exchange value of a medium of exchange back to its function as such a medium and to the theorems concerning the process of valuing and pricing as developed by the general catallactic theory. … no good can be employed for the function of a medium of exchange which at the very beginning of its use for this purpose did not have exchange value on account of other employments.  And all these statements implied in the regression theorem are enounced apodictically as implied in the apriorism of praxeology.  It must happen this way.”