A caution may not be out of place with reference to cases which may occur during the epidemic prevalence of _influenza_. A child is sometimes struck down by it, just as grown persons are sometimes, with great depression, extreme rapidity of breathing, and very high fever, which, passing off in a couple of days, leave a state of great exhaustion behind. It is well to bear in mind that such symptoms have no such grave meaning when influenza is prevalent as they would have at another time; and the knowledge of this fact may serve in some degree to control your anxiety. =Pleurisy.=--It is not possible for anyone, without medical experience, to discriminate between pneumonia, or inflammation of the substance of the lung, and pleurisy, or inflammation of its covering. Some degree of the latter, indeed, very often accompanies the former, and this accounts for the pain which interferes with every attempt of the child to draw a deep breath. When pleurisy comes on independent of affection of the lung-substance, it generally sets in suddenly with severe pain in the chest, and a short hacking cough which causes so much pain that the child tries as much as possible to suppress it. After a few hours the severity of the pain usually subsides, but fever, hurried breathing, and cough continue, and the child, though usually it looks heavy and seems drowsy, yet becomes extremely restless at intervals--cries and struggles as if in pain, and violently resists any attempt to alter its position, since every movement brings on an increase of its sufferings. The posture which it selects varies much; sometimes its breathing seems disturbed in any other position than sitting straight up in bed; at other times it lies on its back, or one side; but whatever be the posture, any alteration of it causes much distress, and is sure to be resisted by the child. The variations of posture depend on the seat of the inflammation; the pain depends on the two inflamed surfaces of the membrane rubbing against each other, and accordingly is relieved not merely by the abatement of the inflammation, but also when either the two surfaces become, as they often do, adherent to each other, or when fluid is poured out into the cavity of the chest, and thus keeps them asunder. I dwell on this, because when fluid is poured out, the most distressing symptoms greatly abate, or even disappear, and parents sometimes put off in consequence sending for the doctor, while yet, if unattended to, the fluid may increase to so large a quantity as to press upon the lung, and so interfere with the entrance of air, or it may, if the mischief is not checked, change into matter, and then have to be let out by tapping the chest, for just the same reason as it may be necessary to open an abscess in any other situation. Whenever, then, symptoms, such as I have described, come on, send at once for medical advice, and do not let some diminution of suffering, or slight general improvement, lead you to delay.