1. The total capacity, middle capacity, and residual air have been determined in 31 adult male patients suffering from tuberculosis of the lungs.

2. The chest volumes have been determined in each case and the normal lung volumes calculated by means of the ratios worked out in a previous paper.

3. In nine patients with incipient tuberculosis, the total lung volume was found within normal limits, whereas the vital capacity was diminished as a result of an increased residual air.

The increase in the residual air was due to less complete expiration, caused partly by diminished movement of the diaphragm, partly by diminished compression of the chest wall. The diminished movement of the diaphragm was, as a rule, most marked on the most affected side. Whether these decreased movements are due to a reflex or to stiffness of the lung tissue we could not determine.

The middle capacity was found practically normal.

4. In twenty-two cases of moderately advanced, and advanced tuberculosis, the total lung volume was in most cases markedly decreased.

The vital capacity was substantially decreased, principally as a result of the diminished total capacity. The residual air was, as a rule, normal, although in a few cases an increase in residual air also contributed to the decrease in the vital capacity.

The middle capacity, on which we do not want to put too much stress, was normal in some patients and considerably diminished in others.

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