Prostitution, in the light of political economy, is far less of an evil than the enforced maternity of wretched and discordant families, which becomes the fountain of an endless flow of crime, while prostitution shows its evils only in the parties immediately concerned, and effectually purifies society in time by arresting the propagation of its most worthless members. In the same manner it may be said that some epidemics are an advantage to society, by cutting off the feeble and worthless constitutions so as to leave a better race. Any one who recollects the history of the Jukes family, and the number of criminals infesting society who were descendants of one depraved pair, will not believe that such a propagation of crime should be permitted. The worthless class should not be allowed to marry, and the criminals whom the state finds it necessary to confine in the penitentiary should be permanently deprived of the power of parentage. Few ever reflect upon the necessary consequences of the growth of population. The great wars, famines, and pestilences as in the past will not be able to keep down population, and where it has free course under favorable circumstances it doubles in twenty-five or thirty years. In two centuries more we shall begin to feel a terrible pressure, and that pressure will be aggravated by the exhaustion of coal mines, of petroleum, of gas, and of forests. In Great Britain alone 120,000,000 tons of coal are annually mined. It may be safely assumed that one thousand to the square mile is about the limit of population of the world, a limit at which population must be arrested. Massachusetts is already within less than a century of its utmost possible limit. It has at this time about 250 to the square mile, and at the American rate of growth it would reach its utmost limit by the year 1950, and begin to realize the crush and crisis of a crowded population, which must either cease to grow or encounter the horrors of famine and social convulsions arising from the struggle for life, or the calamities arising from unfortunate seasons which in China and India have in our own time hurried millions into their graves. If Massachusetts is within sixty years of this collision with destiny, other countries are still nearer the dead line of the coming century. Italy is parallel with Massachusetts and Rhode Island, but Great Britain and Ireland are considerably further advanced. British India and the Netherlands are still further advanced, and half a century, if they had the American ratio of growth, would bring them to their limit, while Belgium's progress would be arrested in thirty years.