Evidently a careful distinction must be made between state provisions which incidentally affect commerce and those which amount to a regulation of commerce, and this distinction depends on the legal definition of commerce. As applied in determining whether a particular act or transaction involves foreign or interstate commerce which is within the control of Congress, or internal commerce which remains within the control of the states, the term has been held to cover the transportation of goods, including the bringing of goods into the state for sale, the transportation of persons into or from the state, the conveyance of messages by telegraph between persons in the state and those in another state or in a foreign country, and, in general, all forms of personal and business intercourse over or across state lines. But the making of contracts is not commerce in this sense.

Foreign and interstate commerce is not limited to the mere transportation of goods, persons, or intelligence across the state lines. The whole transaction from the beginning to the end is one continuous act of commerce. If goods are shipped from a point in one state to a point in another state or in a foreign country; or conversely, if goods are shipped from a point in another state or in a foreign country to a point within the state, the entire transaction is interstate or foreign commerce, and state regulations are no more applicable to the portion of the transaction which takes place within the state than to that which is outside of the state, or which involves the mere passing of the state line. Thus although a navigable river or lake is entirely within the state limits, nevertheless navigation on such river or lake, so far as it involves the transportation of goods along such channel of communication, is interstate or foreign commerce so far as the goods are brought from without the state to a point of destination in the state, or taken from a point within the state to a point without the state. The same principle is applied to transportation over railroad lines, even though they are operated exclusively within the state, if they constitute a portion of a line of transportation for goods brought into or taken out of the state. The same principles apply to transportation of goods through the state between points in other states. Illustrations of the application of these principles will be found in subsequent sections of this chapter.