Acute serofibrinous pleurisy is now almost invariably regarded as due to tuberculosis. In what manner tuberculosis gives rise to it, is, on the other hand, somewhat obscure. As a rule, one has been content to state that the tuberculous infection in some manner produces the exudation. The most obvious and common explanation is that a subpleural tuberculous focus has provoked an irritation of the pleura.
That a local tuberculous focus in the lung or the bronchial glands constitutes an important factor in the genesis of pleurisy is indicated by the fact that a focus of this kind can be detected on the side on which the exudation subsequently arises. If an opportunity presents itself of examining a child a short time before it contracts pleurisy, there are generally found homolateral hilar changes or a homolateral primary focus. Of fifty children examined before the development of pleurisy, forty-eight showed homolateral changes