of living has entirely altered the component parts of our bodies. The pressure of our atmosphere has also much to do with our weight. In your time your bodies consisted of about eighty per cent. of water, as you required a large amount of moisture to enable you to exist. With our atmosphere and with our mode of living we require almost no moisture. Our muscles, our nerves, and our bones are made of a material that is light but very strong. I cannot give you a better illustration to convey to your mind a conception of this substance, than by telling you that we are composed of a material somewhat of the nature of silk. Our brains, our very bones, consist of the same material surrounded by gases. Each nerve, each sinew, each artery, each vein, floats, as it were, in a casing consisting of cells filled with gases. Our lungs are composed of a series of cells made of the finest net-work of gauzy material, through which the atmosphere is inhaled, and the nutriment therein is thus conveyed to the
