In the lung, as in nearly every organ of the body, there exists a large margin of functional reserve which may be called into play when conditions demand. It is this reserve that is utilized when one lung is required to take over the work of both, either because of an extensive pathologic process or as a result of the collapse of one lung induced as a therapeutic measure to afford functional rest. It is commonly stated that the production of even a partial collapse of a diseased lung throws a "strain" on the collateral side, and it is almost as universally accepted and feared that this added strain may in some way favor the spread of the disease to the sound side, or at least may tend to fan into activity a smoldering or quiescent focus of disease.
It is on the basis of such reasoning that the condition