Summary1. The reasons for removing the blood from a hemothorax are given.2. The strange ways in which hemothorax blood may clot are described, and the theo'ries to explain the clotting are discussed.3. The various ways in which heahorax blood may be removed are discussed.4. A brief outline of how hemothorax patients have been treated in New Guinea is given.5. Important practical points concerned in the aspiration of hemo‐thoraces are describe