148 NATURE OF CAPITAL AND INCOME [Crar. IX 
ling” grows into a “tree.” We may, if we choose, consider 
the sapling as one category and the tree as another. In 
this case the “sapling” performs a service at the moment 
it becomes a “tree,” just as the “tree” performs one later 
when it, in turn, becomes “lumber”; but no effect on 
social income is produced, because, if we credit the sapling 
with the value of the tree, we must debit the tree with the 
cost of the sapling. Likewise we may arbitrarily designate 
the moment when a “calf” becomes a “cow,” or when 
“pew” wine becomes “old,” without disturbing the income 
accounts of society; for such events are always two-faced 
and cancel themselves out in the total. We may, in fact, 
mark any stage whatever in the course of production by an 
arbitrary line, and regard the passage across this line as a 
service on the part of the capital on one side of the line 
and a disservice on the part of the capital on the other side. 
§ 4 
The second class of interactions is transportation, or the 
change in place of wealth. It is a very thin line which 
separates this class from the preceding class. Transform- 
ing or producing wealth consists of changing the position 
of its parts relatively to each other ; transporting wealth 
is changing the position of that wealth as a whole. But 
“part” and “whole” are themselves loose and relative 
terms. Bookbinding is a transformation or production of 
wealth ; it assembles the paper, leather, thread, and paste 
into a whole book. Delivering books to a library is trans- 
portation. Yet the library is, in a sense, a whole; and to 
assemble books into a classified and organized library is to 
make a whole out of parts. The distinction between trans- 
formation and transportation is thus merely one of conven- 
ience. Many writers prefer to include them both under 
“production.” We prefer to include them under the less 
ambiguous and more inclusive rubric “interactions,” and 
our object here is not to emphasize their difference, but