In connection with this problem we may again refer to the natural and biological sciences. These have obtained their results, the establishing of laws, by the use of experiment. Having isolated a problem, say the problem of heredity, they make conjectures as to what would happen under changed conditions, and consciously introduce all changes which are conceived as having a possible meaning for the problem. In these sciences the experimenter is not hindered from introducing changes by the consideration that he may spoil his materials. The chemist or entomologist expects to spoil many materials in the course of his tests. Human material is, however, so precious that the experimenter is not justified in assuming the risk of spoiling it. The child is more precious than the problem. The only field in which experiment on the human being is recognized, or rather practiced without recognition, is medicine, where the material is already threatened with destruction through sickness, and the physician introduces an experimental change, say the use of a serum, which gives a chance of preserving life and restoring health. Nevertheless, as the result of a series of experiments on the behavior of animals, one of the psychologists assumed that similar work might be done on the newborn child with no more discomfort than he suffers in having his ears scrubbed and certainly no more damage than he receives from the strains and distortions suffered in the act of being born. I quote from the record of these experiments: On the psychological side our knowledge of infant life is almost nil.... A prominent professor of education once said to us, “You will find when you have taught as many children as I have that you can do nothing with a child until it is over five years of age.” Our own view after studying many hundreds of infants is that one can make or break the child so far as its personality is concerned long before the age of five is reached. We believe that by the end of the second year the pattern of the future individual is already laid down. Many things which go into the making of this pattern are under the control of the parents, but as yet they have not been made aware of them. The question as to whether the child will possess a stable or unstable personality, whether it is going to be timid and beset with many fears and subject to rages and tantrums, whether it will exhibit tendencies of general over or under emotionalism, and the like, has been answered already by the end of the two year period.