[2] Action and co-operation as here described can be observed in everything which has any activity and power of movement. Such is the action and co-operation of the heart and every one of its arteries. The heart acts and the artery uses its coverings or tunics to co-operate; and this is how the circulation of the blood works. It is much the same with the lungs. The air acts by the atmospheric pressure which depends on altitude, and the ribs first co-operate with the lungs, and then the lungs co-operate with the ribs. This is how every membrane in the body breathes. In the same way the meninges of the brain, the pleura, the peritoneum, the diaphragm and all the other coverings of the viscera and their inward structures act and are acted upon and so co-operate, since they are elastic. This is how they come into existence and continue in existence. It is much the same in every fibre and nerve, and in every muscle, even in every cartilage. It is well known that in each of these there is action and co-operation. [3] Every sense too affords an example of co-operation, for the sensory organs, like the motor organs, are composed of fibres, membranes and muscles. But it would be a waste of time to describe how each of them co-operates. We know that light acts on the eye, sound on the ear, smell on the nose, and taste on the tongue, and that the organs respond to these things, thus giving rise to sensation. Can anyone fail to perceive from this that if there were no such action and cooperation with inflowing life in the spiritual organism of the brain, thought and will could not come into existence? For life flows into that organism from the Lord, and because it co-operates the perception is possible of what is thought, likewise what is there judged, concluded and given expression in action. If all that happened was that life acted and the person did not co-operate as if of himself, he could no more think than a block of wood, or than the structure of a church can when a minister is preaching. In this case something like an echo may be experienced as the result of the reflexion of sound from the doors, but no speech. That is what a person would be like, if he did not cooperate with the Lord as regards charity and faith.