Since Quincke's 1 report in 1882, repeated attempts have been made to establish a diagnosis of malignant disease from the character of the cells present in pleuritic or peritoneal exudates. Where bits of tissue are withdrawn by the exploring needle, such a diagnosis may sometimes be made with a fair degree of certainty just as it has been made in the case of tissue obtained in stomach washings, the urine, the feces, etc. The recognition of isolated cancer cells, on the other hand, is extremely uncertain; and in 1900 Widal and Rivaut, 2 after a study of the cells in 600 exudates, concluded that it is difficult to diagnose cancer from such cells, on account of their general resemblance to endothelial cells. In one of the cases to be reported, the presence of many mitotic figures rendered the diagnosis of malignancy almost certain, in the second case their appearance in small numbers