There are several reasons why the minute psychological study of infant life is important.... (1) There are no standards of behavior or conduct for young infants. Our experimental work, which even at the end of two years is just beginning, has taught us that the study of infant activity from birth onward will enable us to tell with some accuracy what a normal child at three months of age can and should do and what additional complexities in behavior should appear as the months go by. Psychological laboratories in many institutions ought to be able to make cross-sections of the activity of any infant at any age and tell whether the streams of activity are running their normal course, and whether certain ones are lagging or have not even appeared. After sufficient work has been done to enable us to have confidence in our standards we should be able to detect feeble-mindedness, deficiencies in habit, and deviations in emotional life. If a proper analysis of the activity streams can be made at a very early age the whole care of the child may be altered with beneficial results.... At present we simply have not the data for the enumeration of man’s original tendencies, and it will be impossible to obtain those data until we have followed through the development of the activity of many infants from birth to advanced childhood. Children of five years of age and over are enormously sophisticated. The home environment and outside companions have so shaped them that the original tendencies cannot be observed. The habits put on in such an environment quickly overlay the primitive and hereditary equipment. A workable psychology of human instincts and emotions can thus never be attained by merely observing the behavior of the adult.... (2) By reason of this defect the study of vocational and business psychology is in a backward state. The attempt to select a vocation for a boy or girl in the light of our present knowledge of the original nature of man is little more than a leap in the dark. High sounding names like the constructive instinct, the instinct of workmanship, and the like, which are now so much used by the sociologists and the economists, will remain empty phrases until we have increased our knowledge of infancy and childhood. The only reasonable way, it would seem to us, of ever determining a satisfactory knowledge of the various original vocational bents and capacities of the human race is for psychologists to bring up under the supervision of medical men a large group of infants under controlled but varied and sympathetic conditions. Children begin to reach for, select, play with and to manipulate objects from about the 150th day on. What objects they select day by day, what form their manipulation takes, and what early habits develop upon such primitive instinctive activity should be recorded day by day in black and white.