Natural Wonders

by Edwin Tenney Brewster

Perhaps you have noticed (if you haven’t, try it—only don’t lie on the damp ground) that when your legs are tired, they rest and stop aching much more quickly if you put your feet up higher than your head. This is, of course, because the blood current coming from the tired muscles, can run down hill, and so most easily drain off the toxins which make the ache. So too, you can keep fresh much longer, whether you are working or playing with the muscles, or sitting still and working your brains over your lessons, if you stand up properly and don’t slouch. When you slouch, you cramp your lungs. The cramped lungs fail to clear the blood. The dirty blood fails to wash brain or muscles clean, and you get tired sooner than you ought. For the same reason, you tire more quickly in bad air. But if you give blood and lungs a fair chance, they will do a lot of resting for you while you are still at work.

But long before we get in the least tired, we get out of breath. Poisons as before, only this time it is largely the carbon dioxid that does the business. The muscle-sugar explodes, and forms the carbon dioxid. The carbon dioxid leaks out into the blood; and the blood, circulating thru the body, carries it to a certain nerve center high up in the back of the neck. This in a sense tastes the carbon dioxid, something as the tongue tastes it in a glass of soda water.

When the nerve center in the neck tastes a little carbon dioxid, it doesn’t say anything. But the moment the taste begins to get strong (which is in less than a quarter minute after one starts running hard) it telephones over the nerves to the lungs: “Here, here, here! What is the matter with you fellows. Get busy. Breathe hard. This blood is fairly sizzling with burnt up sugar!”

Thereupon the lungs get down to work. They breathe as hard and as deep as they can; while the heart, which has also been telephoned of the situation, beats harder and harder, to give the lungs all the blood they can clean, and the working muscles all the blood they can dirty.

If heart and lungs hold their own, nothing in particular happens. But if we keep running on too hard, so that muscles poison the blood faster than the lungs can un-poison it, then the nerve center which is in the back of the neck interferes once more. When it cannot make heart and lungs work faster, it calls off the muscle. Suddenly it gives us such a feeling of loss of breath and suffocation, that we simply cannot run another step. We have to stop. Then heart and lungs catch up on their work.

Curiously enough, getting one’s “second wind” as we say, when the lungs after pumping violently, settle down to working steadily once more tho we still keep on running, and “getting in training” so that we can do all sorts of exercises without getting winded, both these highly desirable conditions depend in part on teaching this “respiratory center” in the neck not to raise so much of a row when it smells a little carbon dioxid in the blood. We train our muscles to do their work; and we also train this nerve center not to get rattled and turn on that feeling of suffocation until it absolutely has to. We get it used to burnt muscle-sugar so that it doesn’t mind the taste as it did.

So, as I say, we live only by just escaping being mildly poisoned. But the curious thing about it is that among these various poisons which would certainly kill us forthwith, if we did not promptly get them out of our bodies, stands, of all things, sugar.

We eat a good deal of sugar in our food. We make a good deal more out of other sorts of food. If we did not make sugar, and have it always on hand in our blood, we could neither work nor live. And yet thousands of persons, every year, die of nothing in the world but sugar poisoning.

Sugar is so very poisonous that we have a special arrangement in our livers for keeping down the amount that at any one time gets into the blood. But for this, a box of candy, or a meal of bread and potatoes would inevitably kill us within three hours. The blood of a full grown man always contains about a quarter ounce of sugar, that is to say, two ordinary lumps. If he has less than two lumps, he begins to starve. If he has more than three or four lumps, his head feels heavy and he cannot keep awake. He begins, in short, to be poisoned. But any one who should get his blood half as sweet as he takes a cup of tea or coffee, would promptly drop into a sleep from which he would never wake up at all.

One thing then that the liver is for is to catch the sugar as it goes by, after a meal, and store it up where it will do no harm. Then it slowly feeds it out again, as the muscles use it up, always keeping the amount in the blood at two lumps. But if we eat or make more sugar than the liver can pack away, then the rest is changed into fat and stowed under the skin and around the muscles. So we store our food as fat, and use it as sugar—fat, luckily, being one of the few things we make in our bodies that are not poisons.