"Man flies from time, and time from man; too soon

In sad divorce this double flight must end."-YOUNG.

three lobes of the right lung and the two lobes of the left lung are shown in their proper positions. g is the windpipe through which air is admitted.

84. Why are the lungs capable of indicating whether an infant found dead has been still-born or not?

Because lungs which have never breathed are heavier than water, and sink; but lungs which have breathed, if only once, are lighter than water, and swim.

85. The lungs, previously to birth, are compressed like a squeezed sponge, and expand whenever the pressure is taken off. The moment they expand the air rushes in by the nostrils and mouth; and the force with which it enters causes the expansion a little beyond the natural state. This acts as a stimulus upon the muscles, which immediately contract, diminish the cavity of the chest, and, in conjunction with the elasticity of the lungs, expel the air till the lungs are again reduced to less than their natural capacity, and this stimulates the antagonists of the former muscles, namely, those which expand the chest, and they assist the pressure of the atmosphere in again filling the lungs. The expansion of the lungs is always produced by their own elasticity, for no muscular apparatus could work so fine a structure; but the expansion of the chest gives room; and the contraction of the chest again occasions the expulsion. Thus the lungs are set going by atmospheric pressure and elasticity; and the action is kept up and regulated by this and muscular force conjointly.

N

86. Why does the chest heave when we breathe?

Because when we inspire the air, the ribs are drawn upward and outward, and the diaphragm at the same time is forced down. When we expire the air, the ribs return to their natural place, whilst the diaphragm is again drawn up.

87. In the accompanying illustration, the front half of the ribs being cut away, the interior of the chest is exposed. CC is the cavity of the chest, empty. DDDD the diaphragm, rising high in the centre

NATURAL HISTORY.

"Life's cares are comforts; such by Heaven designed;

He that has none must make them or be wretched."-YOUNG.

and descending very low at the sides and behind. The white space is its tendonous portion. The lower part is muscle that contracts to draw it downward. AA is the abdomen.

88. What is the liver, and how are its functions performed?

The liver lies horizontally on the right side of the body immediately below the diaphragm, and is protected by the interior ends of the lower ribs. Its function is to secrete the greenish-yellow fluid, the gall or bile, which is conveyed from the liver by a canal called the hepatic duct. On the lower surface of the liver is situated a small pear-shaped bag, the gall bladder, which is also furnished with a duct, called the crystic duct, which unites with the duct from the liver, and forms the common biliary duct.

89. What is the composition of the brain?

The brain is composed of two substances, namely, of a greycoloured pulp, and of a white fibrous texture. The grey pulp is the glandular or active substance, and is made up, like other glands, of minute points or cavities, from which proceed the finest conducting tubes. These tubes, intertwining and uniting in bundles within the brain, are called the cerebral fibres, and they constitute the white substance occupying, for the most part, the central and under portions of the brain. The grey substance lies chiefly on and near the surface, and also in the neighbourhood of those cavities within the brain, which are called its ventricles. The brain is separated by a firm membrane into two distinct organs, the great brain and the small brain. The great brain is situated in the front and upper part of the skull, and its surface is marked by depressions and elevations which, resembling the folds of a garment, are called its convolutions. The small brain lies underneath at the back of the skull; its surface is formed by close layers of the grey substance, presenting a laminated appearFour united roots or stems of the fibrous substance, two from each brain, with distinct portions of the grey or glandular substance at regular intervals interspersed, constitute the spinal cord. Nerves pass out of the brain and spinal cord, and are distributed to every organ of the body.

ance.

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