ABSTRACT
If educational psychologyis to gain a complete understanding of human nature, it must take into account the findings of the science of biology, which traces man’s bodily structures and some of his traits back to remote origins in lower forms of animal life. Biology teaches that the body of an animal of the lowest type is a minute mass of protoplasm — a single cell. This cell is not differentiated into specialized organs such as are present in all the higher animals. It has no organs of sense and no muscles. A unicellular animal exhibits, in spite of its comparative simplicity, the fundamental functional characteristics which appear in elaborate forms in all the higher animals, including man. Four such characteristics can be distinguished. First, a unicellular animal is sensitive; that is, its internal condition is changed when certain external forces act on it. For example, an inner commotion is set up when light strikes a unicellular animal, when certain chemical substances act on it, when it is stimulated by movements of the water in which it lives; or when it comes in contact with a solid object. Second, a unicellular animal is contractile; that is, it is capable of changing its form and, through changes in form, of executing various types of movement. Third, a unicellular animal can assimilate certain substances which the surrounding world supplies as food; that is, it has the power of digesting these substances and converting them into protoplasm. Fourth, a unicellular animal is capable of reproduction. The single cell of which the body of such an animal consists divides under favorable conditions of nutrition and temperature into two cells, each one of which lives after division as an independent individual.
