This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
We have already learned that the body consists of a vast number of cells and fibres, combined to form organs; and that each kind of cell or fibre and each organ has its own peculiar structure, properties, and uses. Except in so far as the blood, passing from organ to organ, carries matters from one to another, and indirectly enables each organ to act upon the rest, we have as yet seen no means by which all this collection of organs is made to work together, so that each shall not merely look after itself, but regulate its activity in relation to the needs or dangers of other parts of the body.
That the organs do co-operate we all know. The lids shut when an object threatens to touch the eye, and (without our thinking about it at all) thrust themselves in the way so as to protect the more tender eyeball. When we are using the muscles of the legs vigorously the muscles of respiration hurry their action, and, consequently, oxygen is conveyed more rapidly to the blood for the supply of the working leg muscles, and the carbon dioxide produced in great quantity by these muscles is quickly removed. When the sole of the foot is tickled the muscles of the thigh and leg, which are not directly interfered with at all, contract and jerk the foot away from its tormentor. Everywhere we find this co-operation among the organs; and it is only by such co-operation that our bodies are able to continue alive. In Ęsop's fable we are told how the arms and jaws declined to work any longer in providing and grinding food for the lazy stomach, and how they soon came to grief in consequence. We might extend the fable, and go on to state how afterwards the stomach made up its mind to digest and absorb just as much food as it wanted for itself, and not bother about supplying those cantankerous arms and jaws, and the moral would be the same: if the stomach ceased to work for the other parts they soon would cease to be able to send food to it, and so it would itself starve in turn.
Of what is the body made up? How do the various kinds of cells, fibres, and organs differ? How does the blood enable each organ to influence the rest?
Give an example showing the co-operation of the organs of the body. Give another example. A third.