The author, who is professor of education in Auckland University College (New Zealand), analyzes in this well written book a vast amount of material relative to the correlation between biologic functions and seasonal variations. He finds that with the exception of linear growth, biologic and constructive psychobiologic functions show a depression at the winter-spring or early spring season. Linear growth, however, is increased at this season. Also, emotional instability, as illustrated in the increase in crime, suicide and insanity, is at its height. He concludes that the human seasonal periodicity is of very complex origin, depending probably on an organic rhythm related to endocrine activity. This, in turn, may be influenced by external factors, one of the most important of which seems to be solar light.