2. When the attempt is made to hold the breath after a forced inspiration, almost everyone at the first trials will allow more or less of the air to escape; that is, they will discover themselves incapable of controlling their own organs of respiration; therefore, a gymnastic exercise for acquiring such control is necessary. This is the exercise which will make us masters of the movements required to produce vocal sounds at pleasure.
3. A slow expiration so controlled as to give time for the air to penetrate into the spirometer, is accomplished, though somewhat unevenly, the first few times, and is perfected with practice.
It results from the above that: 1. We take in less air than we are able to take in; 2. part of this air is lost outside the spirometer; consequently the spirometer registers a pulmonary capacity below that which the lungs actually have; and we shall find that, with practice, the volumetric figure will successively augment. But the pulmonary capacity has not augmented in proportion; it is only that practice has perfected the respiratory movements. Accordingly, the spirometer may serve as an instrument to test the progress made in respiratory gymnastics, and, in the case of those who have already become skilful in its use, it becomes a really valuable instrument for measuring the respiratory capacity.
When we remember that a portion of the air, i.e., 1,200 cubic centimetres, never issues from the lungs, it follows that the respiratory capacity is less by 1,200 cubic centimetres than the pulmonary capacity, which, as we have seen, is on an average upward of 5,000 cubic centimetres (5,370) in the adult man. Hence, the spirometer directly measures the respiratory capacity, and only indirectly the pulmonary capacity.
When women measure their lungs by means of the spirometer, they have difficulty in registering 2,000 cubic centimetres, and men have difficulty in attaining 2,600 cubic centimetres. Instead of which, a man ought to be able to register between 3,800 and 4,000 cubic centimetres.
What keeps the lungs healthy is an abundant aeration with air rich in oxygen, and not impure with carbon dioxide and other poisonous gases. When the pulmonary air-cells are insufficiently dilated, they are predisposed to attack by the bacillus of tuberculosis. Indeed, pulmonary tuberculosis usually begins at the apexes of the lungs, which are less thoroughly aerated, and also usually attacks persons with narrow chests. The treatment of tuberculosis is eminently a fresh-air treatment; tuberculous patients may be benefited and even cured in a remarkable percentage of cases (50 per cent.) if they are exposed day and night to the open air. In this way the relation between free respiration and pulmonary health is demonstrated.
In America at the present time the hygienic rule of sleeping at night, winter and summer, with the windows open, is gaining ground, and even the practice of sleeping in the open air. And the various forms of sport also have the beneficial effect of bringing those who indulge in them into a healthy contact with fresh air, which civilised man has shown a fatal tendency to abandon.
The same exercise which dilates the lungs (the contents) also dilates the thorax (the container). The result is that man ends by acquiring the thorax corresponding to his vocation, or in other words, a thorax corresponding to the life that he leads in consequence of the form of work to which he devotes himself. Shepherds in mountain districts and mountain peasants have the largest thorax, notwithstanding, as we have seen, that they are more scantily nourished. In cities, the maximum average circumference of chest is found among the cart-drivers, and the minimum among university students and in general among those who have grown up in an inclosed environment, with the thorax artificially cramped by the position assumed while writing or reading at a desk; yet this is the class of persons who have abundant nutriment.
Consequently, we find a division of air and bread between different social castes; those who have air, do not have bread, and they possess large lungs, out of proportion to bodies which, being underfed, have been unable to grow; and those who have bread do not have air, and they possess lungs that are insufficient for the needs of bodies that have grown under the influence of abundant nutrition. Consequently, all civilised men are physiologically out of equilibrium, and their physical health is lessened. But those who suffer most from this loss of equilibrium are the studious class, who have nourished themselves upon hopes and opened their minds to great ideas, and deluded themselves into undertaking big enterprises; but in real action they find that they are weak, and that they easily fall into discouragement and depression, and when their will-power forces them onward, their organism responds with nervous prostration and melancholia.