The dangers posed by untutored and unskilled bleeders were noted periodically. In antiquity Galen complained about non-professional bleeders, and in the Middle Ages, Lanfranc (1315), an outstanding surgeon, lamented the tendency of surgeons of his time to abandon bloodletting to barbers and women.[35] Barber-surgeons continued to let blood through the seventeenth century. In the eighteenth and nineteenth centuries, the better educated surgeon, and sometimes even the physician, took charge of bleeding. _Bloodletting and the Scientific Revolution_ The discovery of the blood's circulation did not result in immediate changes in the methods or forms of bloodletting. William Harvey, who published his discovery of circulation in 1628, recognized the value of investigating the implications of his theory. Harvey could not explain the causes and uses of the circulation but he believed that it did not rule out the practice of bloodletting. He claimed that daily experience satisfies us that bloodletting has a most salutary effect in many diseases, and is indeed the foremost among all the general remedial means: vitiated states and plethora of blood, are causes of a whole host of disease; and the timely evacuation of a certain quantity of the fluid frequently delivers patients from very dangerous diseases, and even from imminent death.[36] The English scientist Henry Stubbe brought to the surface what would appear to be an obvious dilemma: How could one bleed to produce local effect if the blood circulated? Stubbe commented in 1671: I do say, that no experienced Physician ever denied the operation of bloodletting though since the tenet of the Circulation of the Blood the manner how such an effect doth succeed admits of some dispute, and is obscure. We the silly followers of Galen and the Ancients do think it an imbecility of judgement, for any to desert an experienced practice, because he doth not comprehend in what manner it is effected.[37] In the early nineteenth century the physiologist Francois Magendie (1783-1855), who argued against bloodletting, showed that the physiological effects of opening different veins was exactly the same, and therefore the choice of which vein to bleed did not affect the procedure.[38] The first serious modern challenges to bloodletting were made in the sixteenth and seventeenth centuries under the leadership of the German alchemist Paracelsus and his Belgian follower, Van Helmont. The medical chemists or iatrochemists espoused explanations for and treatments of diseases based on chemical theories and practices. They believed that the state of the blood could best be regulated by administering the proper chemicals and drugs rather than by simply removing a portion of the blood. Iatrochemistry provided a substitution in the form of medicinals to quell the flow of blood for therapeutic purposes.[39]