The article starts with a brief review of the use and abuse of Hirudo medicinalis. For a long time the word leech was a common name in England for the worm and for a physician, and possibly had its origin in the very old Indo-European stem leg, which is probably also the stem of our Scandinavian terms laege/lege/läkare. It is commonly known, however, that lege and other similar words used for physicians in Europe, both today and in former times, are of Celtic origin. This arouses one's curiosity. With the help of a wellknown American colleague and a Czech physician with a special knowledge of languages, I traced the source of these words back to the great Indo-European family of languages. All the traces pointed to leg-the stem with numerous ramifications in many old and modern languages. From the beginning, leg seemed to be associated with knowledge and wisdom. Tempted by this finding, I followed traces of history, as indicated in words referring specially to physicians in the different European languages. In this article I discuss the significance of the Celtic language in this connection, since in former times it was one of the main branches of the Indo-European family of languages. The old Greek word logos, with its corresponding verb legein containing the same implication as mentioned above, is also said to have some connection with our profession.