In the exercise of their police powers the States may absolutely exclude from their borders only such articles as are in themselves not merchantable or legitimate articles of commerce.

In Bowman v. Chicago & Northwestern R. Co.4 the court say:

4 125 U. S. 465; 8 Sup. Ct. Rep. 689; 31 L. ed. 700.

"Doubtless the States have power to provide by law suitable measures to prevent the introduction into the States of articles of trade, which, on account of their existing condition, would bring in and spread disease, pestilence, and death, such as rags or other substances infected with the germs of yellow fever or the virus of small pox, or cattle or meat or other provisions that are diseased or decayed, or otherwise, from their condition and quality, unfit for human use or consumption. Such articles are not merchantable; they are not legitimate subjects of trade and commerce. They may be rightly outlawed as intrinsically and directly the immediate sources and causes of destruction to human health and life. The self-protecting power of each State, therefore, may be rightfully exerted against their introduction, and such exercises of power cannot be considered regulations of commerce prohibited by the Constitution."

This power of exclusion by the States may not be exercised by the States with reference to articles as a class, unless as an entire class, they are intrinsically unfit for commerce and not merchantable. In all other cases their unfitness for commerce must be determined by inspection and upon reasonable grounds. In the Bowman case the court say: "It has never been regarded within the legitimate scope of inspection laws to forbid trade in respect to any known article of commerce, irrespective of its condition and quality, merely on account of its intrinsic nature and the injurious consequences of its use or abuse."

In no case may the States exclude from their borders or interfere with the importation of such articles as have directly or impliedly been recognized by Congress as legitimate articles of interstate commerce. And, furthermore, it is an established principle that as to articles legitimately the subjects of commerce, the silence of Congress as to them is to be construed as equivalent to a declaration that interstate trade as to them is to be unrestricted.5

These principles have been excellently illustrated with reference to stateLiquor and oleomargarine laws.

5 Leisy v. Hardin, 135 U. S. 100; 10 Sup. Ct. Rep. 681; 34 L. ed. 128.