The principles stated in the preceding sections of this chapter can be rendered more intelligible by a brief statement of some of the important questions which have been decided under them. Soon after the application of steam power to the purpose of propelling vessels, the state of New York granted an exclusive franchise to certain persons to operate steam vessels upon waters within the limits of the state; but the Supreme Court of the United States in Gibbons v. Ogden held this exclusive privilege to be invalid so far as it operated to exclude from the Hudson River steam vessels coming from another state; for although the portion of the Hudson River on which the vessel was navigated is exclusively within the limits of New York, the state statute amounted to a regulation of navigation on that river, and as navigation is included within the meaning of the term commerce, and as, therefore, vessels coming into the waters of New York from another state were engaged in interstate commerce, the restriction which the state of New York had attempted to make was a restriction of freedom of commercial intercourse among the states. Likewise a statute of New York, in effect requiring the payment by steamship companies of a per capita tax upon all passengers brought into the state, was held invalid in Henderson v. Mayor of New York, because transportation of persons as well as of goods is within the meaning of the term commerce, and the state passenger tax amounted to a restriction on foreign commerce. No doubt the state could take proper measures for excluding persons affected with contagious diseases, or who would be likely to become objects of charity, but as Congress has enacted immigration laws covering the whole subject, any state regulation of that character would no doubt now be invalid, as interfering with specific regulations by Congress.

In the proper exercise of its police power, the state may exclude animals having diseases likely to be communicated to other animals, or meat which is unwholesome, but such police regulations must be directly calculated to subserve purposes with reference to which the state can legislate, and not be used as a cloak for regulation of foreign and interstate commerce. Therefore it was held in Railroad Company v. Husen that a statute excluding from a state all cattle brought from another state which may have been subjected to the so-called Texas fever was unconstitutional, because it operated to exclude all the cattle from a certain region without regard to whether they had actually been contaminated with that disease. So in Brimmer v. Rebman it was held that meat inspection statutes, which required that all animals slaughtered for food be inspected while alive within one hundred miles of the place of sale and within a limited time before the meat was offered for sale, were unconstitutional as, in practical effect, preventing the sale within the state of fresh meat from animals slaughtered in another state, regardless of whether such meat was actually unwholesome by reason of diseased condition of the animals slaughtered or the keeping of the meat for an improper length of time after slaughtering.

In the exercise of its police power, the state may unquestionably regulate or prohibit the sale of intoxicating liquors or cigarettes, but as liquors and tobacco are recognized subjects of commerce, it has been held in Bowman v. Railroad Company that state statutes prohibiting the bringing into the state of such articles of commerce are invalid. The regulation of the sale of such goods after they have been brought into the state is another matter, and will be referred to in the next section of this chapter. The state may regulate rates of transportation by common carriers, but state statutes regulating such rates have been held in Wabash, etc. R. Co. v. Illinois not to be applicable to the transportation of goods or passengers so far as such transportation is a part of interstate or foreign commerce. The state may, however, make regulations affecting railroads engaged in interstate or foreign commerce, if such regulations do not amount to an unreasonable restriction on such commerce. Thus statutes requiring that signals be given at highway crossings, or that rates of freight and fare be posted for information of the public, have been upheld. (See Rail-road Co. v. Fuller.)