=Imperfect Expansion of the Lungs.=--Children not premature and perfectly well nourished are yet sometimes feeble, breathe imperfectly, cry weakly, suck difficultly or not at all, and die at the end of a few days. Their lamp of life flickered and went out. Such cases are met with for the most part in conditions similar to those in which children are actually still-born; or now and then they take place when labour has been of unusually short duration, the child hurried into the world too rapidly; while in other instances it is not possible to account for their occurrence. For a long time the nature of these cases was not understood; but rather more than sixty years ago a German physician discovered that air had entered the lungs but imperfectly; that perhaps a third, perhaps even as much as half, of the lungs had never been dilated, but had remained solid and useless; that in consequence the blood was but half-purified, and vitality therefore but half-sustained. The lungs, however, were found to have undergone no real change; they were not diseased, but if air was blown into them the dark solid patches sunk below the level of the surrounding substance, expanded, grew bright in colour and like a sponge from which the water has been squeezed, and crackled, or crepitated as the technical term is, from the air contained within them. We breathe in health so without conscious effort that we never realise the fact that, according to the calculation of most competent observers, the mere elasticity of the lungs, independent even of the elasticity of the chest walls, opposes a resistance to each inspiration equal to 150 pounds avoirdupois in the grown man and 120 in the grown woman. The want of breath puts the respiratory muscles into play: the man takes a deep inspiration, and by this unconscious effort, he overcomes the resistance of the chest and the elasticity of the lungs. The new-born infant feels the same want and makes the same effort; but its muscular power is small, and its inspirations are often so feeble as to draw the air in some parts only into the larger tubes, while many of the smaller remain undilated, and much of the lung continues in the state in which it was before birth. The blood being thus but imperfectly purified, all the processes of nutrition go on imperfectly, the vital powers languish, the inspiratory efforts become more and more feeble, while the elasticity of the lung is constantly tending to empty the small cells of air and to oppose its entrance, and next the temperature sinks and the infant dies.