condary forms of fixed capital situate at _a_, _b_, _c_, _d_,
_e_, has of course a similar history of its own. To represent the full
complexity of the mechanism of industry thus suggested would be
confusing and would serve no purpose here. It is sufficient that we
recognise that at each point A, B, C, D, E, and at each of the points
_a_, _b_, _c_, _d_, _e_, upon the perpendicular lines, stands a
quantity of forms of fixed capital which are gradually worn out in the
work of forwarding quantities of A to B, and quantities of B to C, and
so on. Now if we turn to the point F, where goods pass out of the
productive machine into the hands of consumers, who destroy them by
extracting their "utility or convenience," we shall find in this flow
of goods out of the industrial machine the motive-force and regulator
of the activity of the whole machine.

Let us take an illustration from a single trade, the shoe trade. The
number of boots and shoes purchased by consumers at retail shops and
drawn out from the mechanism at the point F, determines the rate at
which retailers demand and withdraw shoes from wholesale merchants,
assuming for the sake of simplicity that all shopkeepers deal with
manufacturers through the medium of merchant middlemen. If the number
of sales effected in a given time by retailers increases, they
increase their demand from the merchants, if it falls off they lower
their demand. The quantity of goods which retailers will in normal
conditions keep in stock will be regulated by the demand of
consumers.[162] Thus the flow of shoes from D to E, and the quantity
of shoes which at any given time are at the point E, are determined by
the demand of consumers--that is to say, by the quantity or pace of
consumption. If, owing to miscalculation, a larger number of shoes
stands in the retail shops than is required to satisfy current
consumption, or if the flow from D to E is faster than the outflow
from E, this excess ranks as an over-supply of these forms of capital.
Now just as the demand of consumers determines the number of shoes
which stand at E and flow from D to E, so the demand of the retailer
determines the number of shoes which at any time constitutes the stock
of the merchants at D, and the size and number of the orders they give
to the manufacturers at C. Similarly with the earlier processes of
production; the flow of leather from the "tanners" and the quantity of
leather kept in stock are likewise determined b