Dieulafoy's aspirateur, which the author has now used in a very large number of cases, will be found the best method yet devised of safely removing the fluid in cases of serous effusion. But in severe cases of empyema the pus is sure to be reproduced in the great majority, and then a free incision, with strict antiseptic precautions, will be needed, and subsequent free drainage. The author has used with great benefit silver tubes, like long narrow trachea-tubes, with broad shields, to insure free drain. FOOTNOTES: [139] Both in _Guy's Hospital Reports_, second series, vol. ii. [140] _Edinburgh Medical Journal_ for June 1866. CHAPTER XI. OPERATIONS ON ABDOMEN. PARACENTESIS ABDOMINIS.--To withdraw fluid from the abdominal cavity is an exceedingly simple operation in itself, though certain precautions are necessary to render it safe. _Trocar._--The usual instrument used to be a simple round canula with a trocar, the point of which should be very sharp, and in the shape of a three-sided pyramid. It should be about three inches in length, and a quarter of an inch in diameter. It may for convenience have an india-rubber tube fixed to its side or end, for the purpose of conveying the fluid to the pail or basin, but any other additions or alterations have not been improvements. Lately surgeons have been diminishing the size of the tube so as to withdraw the fluid more slowly, and taking many precautions to insure the wound being kept aseptic. _Where to tap._--In the linea alba, midway between the umbilicus and pubes, or rather nearer the umbilicus. Here, there are no muscles nor vessels, the opening is a dependent one, and the bladder is quite out of the way of injury. _N.B._--It is a wise precaution, in every case where there is a possibility of doubt as to the state of the bladder, to pass a catheter. I have myself known at least one case in which a surgeon was asked to tap an over-distended bladder, as a case of ascites.