gratifications, not by such a mere series of quantitative
increments, but by an enlarging area. We may draw a series of
concentric circles, beginning with the smallest, and let this
central area inclose the most necessary forms of consumers'
wealth. When we draw a second and larger circle, we inclose
between it and the first one a zone which includes those
forms which come next in importance. By continuing to draw
circles we reach an outermost one which bounds a zone in
which are included the least important of the consumer's
acquisitions. These are the things which he gets with his
costliest increment of labor, and the things which lie beyond
the circle last drawn would not pay for the sacrifice which
acquiring them would cost. In the accompanying figure the
fifth zone includes these "marginal" forms of wealth.

_How Isolated Men measure Final Utility._--If a cave dweller possesses
a store of one hundred measures of nuts, he measures the final utility
and the value of this store in the manner which we have described. If
he were to be deprived of the whole stock, he might starve, but this
fact does not afford the basis of the value which he puts on the nuts.
He measures the importance of this consumers' wealth specifically. He
tests the effect of losing one measure and no more, and finds that he
could lose the single measure without suffering greatly. The
difference between having an appetite fully satiated and having it
very nearly so is not serious.

[Illustration]

Let _AD_ represent the savage's total supply of food. _AB_ will
represent the utility of the first unit; _CD_ of the hundredth. If we
supply the food unit by unit, the utility of the successive increments
will decline along the curve _BC_. When the man has a hundred units of
food, no one unit of it is worth any more than the last one, since if
any one were taken away, the last one could be put in the place of it.

The _total absolute utility_ of the food is measured by the area
_ABCD_, but the total _value_ will be represented by the rectangle
_ADCE_. The area _EBC_ measures the surplus of utility contained in
the earlier units in the series.

_The Motive for measuring Values in Primitive Life._--Even the cave
dweller would have to measure values, and would thus have to apply the
principle of final utility, because he would need to spend his limited
productive energies in the way that would do him