The value of Traube's semilunar space in differential diagnosis is briefly discussed in modern texts. The statement usually found is that the tympany is replaced by dulness in pleurisy. Cabot1 says that it "is of very little value in diagnosis. This tympanitic area is obliterated in many pleuritic effusions (not in all)." In this connection the following history is of value:
A boy with pneumonia continued to have fever and severe general symptoms after the time of the anticipated crisis. Pleurisy, possibly empyema, was considered.
Physical examination showed a normal tympanitic semilunar space. Next day, before tapping, the same condition was found. After withdrawing about one-half pint of pus, the space was dull as far as the lower boundary of the pleural sinus. This last examination was not more than fifteen minutes after the second examination when tympany was found. During this interval the patient had taken neither liquid