To start with, this machine works in the very simplest fashion. It uses up its motive power as fast as it acquires it. Energy flows in and immediately flows out again in another form. The organism is like a pipe or a vessel without a bottom, so that its contents cannot be stored. The lower organisms which obey tropisms are such bottomless vessels. They are continually and inevitably subjected to the same attractions and repulsions and have no means to withstand them. But at a certain stage of evolution--how? why? Driesch replies: Entelechy!--a new part is developed in the machine, something like the cam on a cogwheel which forces it to come to rest. Or, to keep to the earlier simile, the bottomless vessel acquires a bottom with a tap that can be opened and closed. With this arrangement the organism is able to store the energy it has received and then to make use of it according to its needs, to do much more or much less work with it, to achieve much greater or much smaller effects, than it would be capable of doing with the amount of energy it receives from outside in a given unit of time. It is obvious how much more efficient the organism becomes if it can store up energy and can adapt to its needs the amount used up. This new part of the machine is Inhibition. It appears early, and takes part in the general development of the organism; it is indeed the strongest factor in this development. Before Inhibition intervenes the organism has only one response to stimulus: reflex action. This is of the character of an electric discharge. It may be stronger or weaker, but is uniform in kind. It varies quantitatively but not qualitatively. In the lower organisms it is a contraction of the cell protoplasm, a movement. In the higher organisms, in which the life processes are carried out on the principle of the division of labour and which have developed various organs for this purpose, each organ performs the action of its specific function; the muscle contracts, the nerve sends out a nervous impulse, the gland forms a secretion, and so on. All reflex actions have this in common, that they serve no other purpose than that of relaxing tension in the organism. They do not imply any co-ordinated effort to promote the comfort and the welfare of the living being. They cannot fulfil any complicated task. They exhaust the organism which, after a series of reflex actions, becomes insensitive to stimuli and must rest for a time before it can react again.