+21+. The interior being, whose existence was vaguely felt, was recognized by early man in many common experiences. Certain phenomena were observed that seemed to be universal accompaniments of life, and these, by a strictly scientific method of procedure, were referred to an inward living thing. It was hardly possible for early observers not to notice that when the breath ceased the life ceased; hence many peoples have regarded the breath as the life, and as the form of the interior being, and in many languages the words for 'soul' and 'spirit' are derived from the word for 'breath'.[20] The breath and therefore the soul of a dying man might be received (inhaled) by any person present; it was sometimes obligatory on a son to receive his father's last breath--he thereby acquired the father's qualities.[21] +22+. Another accompaniment of the body that attracted the attention of early men was the shadow, for which the science of that day, unacquainted with optical laws, could account only on the supposition that it was a double of the man, another self, a something belonging in the same general category with the breath-soul, though usually distinguished from it.[22] The shadow was regarded as a sort of independent objective being, which might be seized and destroyed, for example, by a crocodile, as the man passed along a river bank; yet, as it was the man, its destruction involved the man's death.[23] The soul, regarded as a shadow, could not cast a shadow. Similarly one's reflection in water was regarded as a double of him.[24]