States from this exclusive power of Congress is not always
distinctly marked, and oftentimes it is not easy to determine on which
side a particular case belongs. Judges not infrequently differ in
their reasons for a decision in which they concur. Under such
circumstances it would be a useless task to undertake to fix an
arbitrary rule by which the line must in all cases be located. It is
far better to leave a matter of such delicacy to be settled in each
case upon a view of the particular rights involved." Thus the way was
left clear to vary the principle of interpretation according to the
color of the citizens whose rights might be involved.

In view of the subsequent decisions in separate car cases, moreover,
the following portion of Justice Waite's opinion as to a clause in the
law involved in the case of _Hall_ v. _DeCuir_ is unusually
interesting. "It does not act," said he, "upon the business through
the local instruments to be employed after coming within the State,
from without or goes out from within. While it purports only to
control the carrier when engaged within the State it must necessarily
influence his conduct to some extent in the management of his business
throughout his entire voyage. We confine our decision to the statute
in its effect upon foreign and interstate commerce, expressing no
opinion as to its validity in any other respect."[28]

With the rapid expansion of commerce in the United States and the
consequent necessity for regulation both by the State and the United
States, no power of Congress was more frequently questioned than that
to regulate commerce and no litigant concerned in such constitutional
questions easily escaped the consequences of the varying
interpretation given this clause by the United States Supreme Court.
The court, of course, accepted as a general principle that there are
three spheres for the regulation of commerce, namely: that which a
State cannot invade, that which the State may invade, when Congress
has not interfered, and that which is reserved to the State in
conformity with its police power. But as late as 1886 the
nationalistic school found some encouragement in the decision of the
_Wabash, St. Louis and Pacific Railway Company_ v. _Illinois_[29]
given by Justice Miller. He said: "Notwithstanding what is there said,
that is, in the decisions of _Munn_ v. _Illinois; C. B. and Q. R. R.
Company_ v. _Iowa_, and _Peik_ v. _Chicago and N. W. R. R. Co._,[30]
this cou