As soon as possible after the beginning of this work, a definite start was made toward determining the cause of feeble-mindedness. After some preliminary work, it was concluded that the only way to get the information needed was by sending trained workers to the homes of the children, to learn by careful and wise questioning the facts that could be obtained. It was a great surprise to us to discover so much mental defect in the families of so many of these children. The results of the study of more than 300 families will soon be published, showing that about 65 per cent of these children have the hereditary taint. The present study of the Kallikak family is a genuine story of real people. The name is, of course, fictitious, as are all of the names throughout the story. The results here presented come after two years of constant work, investigating the conditions of this family. Some readers may question how it has been possible to get such definite data in regard to people who lived so long ago. A word of explanation is hence in order. In the first place, the family itself proved to be a notorious one, so the people, in the community where the present generations are living, know of them; they knew their parents and grandparents; and the older members knew them farther back, because of the reputation they had always borne. Secondly, the reputation which the Training School has in the State is such that all have been willing to coöperate as soon as they understood the purpose and plan of the work. This has been of great help. Thirdly, the time devoted to this investigation must not be overlooked. A hasty investigation could never have produced the results which we have reached. Oftentimes a second, a third, a fifth, or a sixth visit has been necessary in order to develop an acquaintance and relationship with these families which induced them gradually to relate things which they otherwise had not recalled or did not care to tell. Many an important item has been gathered after several visits to these homes. Chapter IV will throw still more light on the method used. If the reader is inclined to the view that we must have called a great many people feeble-minded who were not so, let him be assured that this is not the case. On the contrary, we have preferred to err on the other side, and we have not marked people feeble-minded unless the case was such that we could substantiate it beyond a reasonable doubt. If there was good reason to call them normal, we have so marked them. If not, and we are unable to decide in our own minds, we have generally left them unmarked. In a few cases, we have marked them normal or feeble-minded, with a question mark. By this is meant that we have studied the case and after deliberation are still in doubt, but the probabilities are “N” or “F” as indicated. The mere fact of the doubt shows, however, that they are at least border-line cases.