The general power to regulate commerce is in strict analysis a part of the police power, and, as has already been indicated in the discussion of that subject (see above, § 48), the states may regulate rates charged by common carriers for the transportation of persons or goods. In some states boards of commissioners have been especially created to exercise a particular supervision over railroad, express, telegraph, and other kinds of corporations engaged in business affecting commerce. Indeed, regulations as to the use of highways, the construction of bridges, the navigation of public waters, and the like, are instances of police regulation principally affecting commerce. Were it not for the limitations upon state power, involved in the provisions in the clause of the federal constitution to be hereafter discussed, which gives Congress certain powers as to the regulation of commerce, there would be no necessity for any separate or particular treatment of this subject, but as the powers of the state are greatly restricted in this respect by that provision it is necessary that the division of powers between the federal government and the governments of the states be considered in some detail.