An organism is a continuous dynamism, a pattern of activity, basically electrochemical, but capable also of large, concerted forms of action with further priniciples of of organization. Its round of functions is continuous, and every constituent action in it, every chemical transformation osmotic exchange, contraction of muscle, discharge from glands, etc., is more or less finely adjusted to the immediate situation created by the environment. Many of these activities are internal to the organism, so the direct environment of the tissues engaged in them is composed of other parts and products of the same system. Environment is, in fact, a relative concept.
The active structures in any metazoic organism are incredibly detailed, and its activities are usually composed of smaller and smaller complete cycles of action, in subordinate but functionally distinct structures. each active unit, be it a single cell or an integral complex, has its direct environment as long as it exists, i.e., performs. All vital action, whether of the organism as a whole in its surroundings or of an organ internal to it, is interaction, transaction, in which the functioning unit has the fine control and the medium in which it maintains itself has the gross control; that is, the latter determines what is given, former what is taken.
— Susanne Langer