In the treatise on easily procurable remedies ascribed to Galen,[734] in which we have already seen evidence of later interpolation or authorship, some recipes are concluded by such expressions as, “This has been experienced; it works unceasingly,”[735] or “Another remedy tested by us in many cases.”[736] This became a custom in many subsequent medical works, including those of the middle ages. One recipe is introduced by the caution, “But don’t cure anybody unless you have been paid first, for this has been tested in many cases.”[737] But we are left in some doubt whether we should infer that remedies tested by experience are so superior that they call for cash payment rather than credit, or so uncertain that it is advisable that the physician secure his fee before the outcome is known. In the middle ages the word _experimentum_ was used a great deal as a synonym for any medical treatment, recipe, or prescription. Galen approaches this usage, which we have already noticed in Pliny’s _Natural History_, when he describes “a very important experiment” in bleeding performed by certain doctors at Rome.[738] [Sidenote: Galen’s influence upon medieval experiment.] Indeed Galen appears to have exerted a great influence in the middle ages by his passages concerning experience in particular as well as by his medicine in general. Medieval writers cite him as an authority for the recognition of experience and reason as criteria of truth.[739] Gilbert of England cites “experiences from the book of experiments experienced by Galen,”[740] and we shall find more than one such apocryphal work ascribed to Galen in the middle ages. John of St. Amand seems to have developed seven rules[741] which he gives for discovering experimentally the properties of medicinal simples from what we have heard Galen say on the subject, and in another work, the _Concordances_, John collects a number of passages about experience from the works of Galen.[742] Peter of Spain, who died as Pope John XXI in 1277, cites Galen in his discussion of “the way of experience” and “the way of reason” in his _Commentaries on Isaac on Diets_.[743] We have already suggested Galen’s possible influence upon Albertus Magnus, and we might add Roger Bacon who wrote some treatises on medicine. But it is hardly possible to tell whether such ideas were in the air, or were due to Galen individually either in their origin or their transmission. But he made a rather close approach to the medieval attitude in his equal regard for logic and for experimentation. [Sidenote: His more general medieval influence.]