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Clinical charts are made to be filled up with the records of temperature; lines drawn from point to point, as the rise and fall are noted, give often very characteristic curves. The accompanying illustration is taken from a typhoid case:

CHAPTER V.

The lungs and air-passages-Respiration: its mode, object, modifications, disorders-The atmosphere: its vitiation and renovation -Ventilation, natural and artificial-Warmth-Modes of heating.

We have seen that the blood undergoes in the lungs a process of purification, rendering it fit for renewed use. To understand how this is accomplished, one must know something of the construction and working of the respiratory organs, the chief of which are the lungs, trachea, and muscles of the chest.

The lungs themselves are of a sponge-like substance, composed of air-cells lined by a network of minute blood-vessels. These blood-vessels are the subdivisions of the pulmonary veins and arteries. A series of bronchial tubes connect the air-cells with the external air, those of each lung uniting into a single bronchus, and the two finally with each other, to form the trachea, or windpipe. Each lung is enveloped in a delicate membrane called the pleura. This is, at the root of the lung, folded back so as to form also a lining to the chest. It secretes a fluid which keeps it constantly moist, and enables the two surfaces to slide easily against each other.

The chest is separated from the abdominal cavity by a muscular partition-the diaphragm-which alternately rises and falls, as its fibers contract and relax. The motion is involuntary, but partially under control. As the capacity of the chest is increased by the descent of the

diaphragm, the additional space is filled by air, sucked in through the trachea and bronchi, and expanding the

[graphic][subsumed][subsumed]

FIG. 7.-The cavity of the chest, showing the positions of the heart and the lungs: 4,left lung; B, heart; D, pulmonary artery; E, trachea or windpipe.

elastic cells. As the diaphragm rises, this extra supply of air is forced out again. The size of the thoracic cavity is still further affected by movements of the intercostal muscles, which elevate and depress the ribs. By these muscular actions, and the consequent expansions and contractions of the lungs, the alternate inspirations and expirations are produced which we call breathing or respiration. The lungs are not completely filled and emptied by each respiration. A certain amount of air is stationary in them. The additional supply drawn in

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