The idea of organism, which of recent years has bulked so largely in scientific, and especially in biological, theory has been developed mainly in reference to living organisms, and has been extended to cover such systems as human societies, crystals, molecules and atoms—and indeed the whole universe has been interpreted as an organism. This use of the term, however, includes different ways in which parts may be together in a system. The belief that the principle of organism has been wrongly extended to explain certain co-ordinations of vital processes which require a different type of explanation is the reason for this addition to the immense literature on the subject of organism.