Of the three things that are indispensable for the subsistence of man,—namely, air, water, and food—the first is the most important. Hence it is that God has created it in such large quantities as to make it available to all of us for nothing. Modern civilisation, however, has rendered even fresh air somewhat costly, for, in order to breathe fresh air, we have to go out of towns, and this means [Pg 15] expense. The residents of Bombay, for instance, distinctly improve in health in the air of Matheran or, still better, of the Malabar Hills; but they cannot go to these places without money. Hence, in these days, it would be hardly true to say that we get fresh air gratis, as we used to in the old days. But, whether fresh air is available gratis or not, it is undeniable that we cannot get on without it. We have already seen that the blood circulates over the body, returns to the lungs, and after being purified, starts on its round again. We breathe out the impure air, and take in oxygen from the outside, which purifies the blood. This process of inspiration and expiration goes on for ever, and on it depends man’s life. When drowned in water we die, because, then we are unable to let out the impure air in the body and take in pure air from outside. The divers go down into the water in what is known as a diving bell, and they take in fresh air through a tube which leads to the top. Hence it is that they are able to remain under water for a long time. It has been ascertained by experiments that no man can live without air for as long as five minutes. We often hear of the death of little children, when they are held so close to the bosom by ignorant mothers as to make it impossible for them to breathe. [Pg 16]