_The Tonnage Laws_ prescribe the rate of tonnage duties that shall be levied on vessels entering American ports. Tonnage duties, as the name indicates, are a form of taxation calculated on the basis of the tonnage admeasurement of the vessel; they are levied on American as well as foreign ships, though the rate is higher on the latter than on the former. Sometimes they have been higher on the vessels of some foreign countries than on those of others, in which case they are known as discriminating tonnage duties. Such discriminating duties are employed for the purpose of favoring the commerce of those nations which extend us commercial privileges and for shutting out or restricting that of nations which discriminate against our trade. In pursuance of the power to regulate foreign commerce, Congress prohibits foreign vessels from engaging in the coasting trade, and permits only citizens of the United States to serve as masters on vessels registered under the American flag. Formerly only American-built vessels could be registered, but in 1914, after the outbreak of the great war in Europe, Congress passed an act allowing ships built in foreign yards, when owned by American citizens, to be registered under the American flag; and more than 100 such vessels have been so registered. _Immigration._--By virtue of the commerce power Congress has enacted a series of immigration laws imposing restrictions on the coming of immigrants to our shores. For a long time immigration from Europe was encouraged rather than restricted, but within recent years so many undesirable persons have found their way to America that Congress has been led to pass various laws designed to shut out the worst of them and admit only the desirable ones.[42] [42] According to the report of the commissioner general of immigration, 1,218,480 immigrants arrived in the United States during the year 1914. Of those who applied for admission into the country, more than 33,000 were turned back. In 1916 the number of arrivals dropped to 366,748; in 1920 it was 430,000. First of all, the immigration laws exclude convicts, insane persons, paupers and those likely to become paupers, persons suffering with dangerous, loathsome, and contagious diseases; epileptics, persons afflicted with tuberculosis, idiots, feeble-minded persons, polygamists, anarchists, immoral persons, and others of this character.