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Published data on the normal blood picture in adolescence are relatively scarce and show considerable disagreement.* In some instances the observed differences undoubtedly are attributable, at least in part, to the difference in the altitude at which the subjects were residing; in others no such ready explanation is available. Furthermore, in some of these data a wide range of hemoglobin values and red cell counts is reported for each age group. The question may be raised whether such marked differences represent normal variations and should be expected to occur in a group of subjects all of whom are in superior health. In September, 1947, and again in 1949, we had the opportunity of studying the blood picture of a highly selected group of healthy rural youths. These were the 4-H Club boys and girls who had been chosen by the local physicians as the health champions of their respective counties

THE CHANGES in composition which the blood of infants undergoes during the first year of life have been extensively investigated. The excellent reviews of previous studies, included in the reports by Mackay (1931) 1 and Faxen (1936-1937), 2 obviate the necessity of a survey of the literature in the present paper. These reviews point out the many factors which have been suggested as influencing the blood picture and suggest that hypochromic anemia may be a common occurrence in young infants. Considerable doubt remains, in consequence, as to what constitutes the normal blood picture in infants and what may be considered as the limits of physiological variation. The present study was undertaken for the purpose of helping to establish normal hematologic standards for infants residing in Minnesota and of investigating the influence of certain factors on the blood picture. PROCEDURE The study was conducted at two well-baby clinics in St. Paul