NO class of cases are more perplexing than those involving the distinction between the power of Congress to regulate foreign or interstate commerce and the so-called police power of the States. It has always been conceded that there were many kinds of laws, such as quarantine laws, health laws, etc., operating upon foreign or interstate commerce, which were within the power of the States. How are such laws to be distinguished on principle from regulations of foreign or interstate commerce within the exclusive power of Congress? On this point the more recent cases are very unsatisfactory. While these cases almost always commend themselves to our common sense as actual decisions upon the facts, the reasoning upon which the decisions are based is meagre and unsatisfactory; indeed, very little general reasoning is attempted. The court almost invariably confines itself to a decision upon the facts involved.
The cause of this hesitancy of the judges to lay down general principles upon the distinction between laws affecting foreign or interstate commerce, which are within the powers of the States, and those which are regulations of foreign or interstate commerce, and within the exclusive power of Congress, is, in the opinion of the writer, to be ascribed to the confusion in which the law was left by