In either of the above cases, both with an overworked stomach and an overworked heart and lungs, the complaint is very apt to be, “Why am I so tired when I have done nothing to get tired?” The answer is, “No, you have done nothing outside with your muscles, but the heart and lungs and the stomach are delicate and exquisite instruments.  You have overworked them all, and such overwork is the more fatiguing in proportion to what is done than any other form, except overwork of the brain.”  And the overtired stomach and heart and lungs tire the brain, of course.

Of the work that is given to the brain itself to overtire it we must speak later.  So much now for that which prevents the body from keeping rested inside, in the finer working of its machinery.

It is easy to find out what and how to eat.  A very little careful thought will show us that.  It is only the plain common sense of eating we need.  It is easy to see that we must not eat on a tired stomach, and if we have to do so, we must eat much less than we ordinarily would, and eat it more slowly.  So much good advice is already given about what and how to eat, I need say nothing here, and even without that advice, which in itself is so truly valuable, most of us could have plain common sense about our own food if we would use our minds intelligently about it, and eat only what we know to be nourishing to us.  That can be done without fussing.  Fussing about food contracts the stomach, and prevents free digestion almost as much as eating indigestible food.

Then again, if we deny ourselves that which we want and know is bad for us, and eat only that which we know to be nourishing, it increases the delicacy of our relish.  We do not lose relish by refusing to eat too much candy.  We gain it.  Human pigs lose their most delicate relish entirely, and they lose much—­very much more—­than that.

Unfortunately with most people, there is not the relish for fresh air that there is for food.  Very few people want fresh air selfishly; the selfish tendency of most people is to cut it off for fear of taking cold.  And yet the difference felt in health, in keeping rested, in ease of mind, is as great between no fresh air and plenty of fresh air as it is between the wrong kind of food and enough (and not too much) of the right kind of food.

Why does not the comfort of the body appeal to us as strongly through the supply of air given to the lungs as through that of food given to the stomach?  The right supply of fresh air has such wonderful power to keep us rested!

Practical teaching to the children here would, among other things, give them training which would open their lungs and enable them to take in with every breath the full amount of oxygen needed toward keeping them rested.  There are so many cells in the lungs of most people, made to receive oxygen, which never receive one bit of the food they are hungry for.

There is much more, of course, very much more, to say about the working of the machinery of the inside of the body and about the plain common sense needed to keep it well and rested, but I have said enough for now to start a thoughtful mind to work.