In general, with reference to barter, this point is significant. The money economy has made barter _easier_ rather than harder. It has made possible a host of refinements in barter, which make it at many points more convenient and cheaper than check or money exchanges. It is common to find our present methods of conducting foreign trade described as a "system of refined barter," which indeed, from the standpoint of the present issue, it is: bills of exchange are neither money nor bank-credit! Where bills of exchange are used in internal trade extensively--as in Germany, where they pass from hand to hand in several transactions before being discounted at banks[202]--we have a highly important substitute for money and deposits, which functions as barter,--flexibility of substitutes for money and deposits is strikingly evident. The feature of the money economy which has thus refined and improved barter is the _standard of value_ (_common measure of value_) function of money.[203] This standard of value function, be it noted, makes no call on money itself, necessarily. The _medium of exchange_ and "_bearer of options_" functions of money are the chief sources of such additions to the value of money as come from the money-use. But the fact that goods have money-prices, which can be compared with one another easily, in objective terms, makes barter, and barter-equivalents, a highly convenient and very important feature of the most developed commercial system. And so we reject another essential assumption of the quantity theory.[204] CHAPTER XII VELOCITY OF CIRCULATION For the quantity theory, it is important to treat velocity of circulation of money and of deposits, as self-contained entities, really independent factors. This is true of Fisher's theory. It is particularly necessary that V and V' should vary from causes unconnected with M and M'. The V's are to be a sort of inflexible channel, through which M and M' run in their influence on the passive P, which is to rise or fall proportionately with them. If an increase of M or M' should lead to a reduction in the V's, if people, having more money available, should be less assiduous in using every bit of it in effecting exchanges, then P would not rise in proportion to the increase in M. Complete demonstration of Fisher's thesis, therefore, requires the proof of the negative proposition that V does not change as a consequence of changes in M or M'. This proof Fisher finds in the contention that the V's are fixed by the habits and conveniences of individuals, whence they are not influenced by such a cause as a change in the amount of money.[205]