Sec. 5] SUMMARY OF PART III 313

of the sapling disappears at BC, but there appears in its
stead the capital-value of the tree. The change from one
to the other is evidently entirely nominal, and it is possible,
 by drawing any other vertical line than BC, to create
an “interaction” simply by calling the portion on the two
sides of this line by different names.
When, as in Figure 25, a series of curves is constructed
and superimposed to represent the income from any specified
 group of capital instruments, the sum total of the income
is evidently represented by the entire series of teeth in the

 

Fic. 25.

top curve. These teeth form a physical picture of the
“outer fringe” of services, which was discussed In
previous chapters. If in the diagram we omit the uppermost
 layer of capital, the curve remaining immediately
below this layer will then be the outer fringe for the entire
series of capital instruments below it. We may proceed
 step by step in either direction, leaving off an tem of
capital or taking one on. In every case the outer fringe
of teeth will represent the sum total of income for the group

of capital represented below it.