In his introductory textbook, Philosophy of natural science, Hempel presents, as an illustration and a starting point for an analysis of the processes of inventing and testing scientific theories, an account of the researches of Semmelweis the Hungarian physician who, in the middle of the xixth century, discovered the cause of puerperal fever and an effective method of prevention. The account does not involve anything that is factually untrue, but it is quite succinct, leaving out many important aspects of the (...) case. Our thesis is that, although those omissions are justified in view of the aims of the account, they are also convenient to Hempel, because they help to propagate an image of science which goes much beyond the processes of invention and test. It is an image which reflects the positivist conception of science, and thus, whatever the intentions of the author, contributes to the dissemination and strengthening of that conception, but which, at least in this case, does not correspond to reality. To demonstrate the thesis, we give an account of the parts of Semmelweis's story omitted by Hempel, and we show how they do not fit in with the positivist image of science. Along the way, we distinguish three types of critique of positivist historiography: the Kuhnian, the post-modern, and the engagé. In the conclusion, we present some considerations concerning the medical research of today. -/- . (shrink)