In concrete eugenic practice it seems probable that most can be accomplished for the present by striving to limit the multiplication of the undesirable, dependent, or dangerous elements of the social group. There can be less uncertainty here. The social organization has already marked certain kinds of individuals as unfit and unworthy, whose liberty must be limited in many directions for the social welfare. This aspect of the matter can be put upon a dollars and cents basis very clearly, and this is apparently the only relation that affects a good many people. Why should the able and worthy and thrifty members of society be compelled to pay, as they are in this country alone, $100,000,000 annually, not to mention the vast sums voluntarily contributed toward "charitable" purposes, for the support of the criminal and pauper and defective classes who themselves contribute nothing of value and whose very existence is evidence of criminal disregard of the right of every individual to be well born, into a healthy and sane life? The only answer, if it be an answer, is--because the competent are willing to foot the bill. Millions for tribute but not one cent for defense. And yet a penny's worth of defense outweighs a million's worth of cure. In the practice of Eugenics the greatest caution must be exercised. All eugenic practice must be tested by the most careful and scrutinizing scientific methods. Mendelian heredity gives a different answer from Job's to his own query: "Who can bring a clean thing out of an unclean?" It also makes clear how it may often happen that it needs but three generations to go from Fifth Avenue to the Bowery, and back again. Many so-called criminals may be anachronisms, some only modificationally bad. But there are many cases, many practices, regarding which there can be no doubt: the Eugenist says, treat these, and let the doubtful cases alone until as a result of the increase of knowledge there is no doubt. And while it is easy to say that we _believe_ the criminal or the insane are the products of a wrong environment, it is also easy to say that we believe they are not. What the Eugenist demands is _knowledge_, then belief, and action based thereon.