Absence of mesothelial cells from tuberculous pleural effusions.

It is a commonplace of clinical teaching that tuberculous pleural effusions contain a high proportion of lymphocytes. This was one of two characteristics noticed by Widal (Widal and Ravaut, 1900), the other being an absence or scarcity of mesothelial (" endothelial ") cells. This second feature is more constant than the first, but for some reason has escaped being generally known. Looking back over stained films of pleural effusions from proved cases of tuberculosis, we found no case in which mesothelial cells were numerous enough to figure in an ordinary differential count. This feature is therefore much more constant than the lymphocytosis. We felt that it would be worth while to publish the data, since it appears that tuberculosis can be practically excluded as the cause of an effusion that contains numerous mesothelial cells.