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Medieval Contributions to the Search for Truth in Clinical Medicine
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Perspectives in Biology and Medicine 43.4 (2000) 530-540

Walter J. Daly * and D. Craig Brater

Galen's essay On Medical Experience was lost until 1931, when it was rediscovered in Arabic in the library of Aya Sophia in Istanbul [22]. In On Medical Experience, Galen set up an imaginary debate between a physician who based his practice on experience alone and another who used reason alone. Each made good points, and Galen concluded that both experience and reason were needed. Rules for proving whether a given treatment had real efficacy seem not to have been mentioned by either Hippocrates or Galen.

Buried in Peter of Spain's commentary on the Dietary of Isaac is a logic-based discussion of the ways to find truth, the "way of reason" (via rationis) and the "way of experience" (via experimenti). Peter's discussion closely follows Galen's essay On Medical Experience. He noted that via experimenti depends on the senses, via rationis on the intellect; experimentum is not argumentative, ratio is; experimentum is inductive, ratio is syllogistic; experimentum proceeds from a fact, ratio from no new information. He concluded that experimentum without ratio was lame, and ratio not based on experimentum faulty [10]. John of St. Amand expressed the same conclusion a bit later: "Experimentum sine ratione debile est, sic ratio non juncto experimentum sibi" [19].

Peter's solution was a set of rules for determining efficacy in therapeutics [10, fol. 21v; 23]:

1. The medicine to be tested should be pure. Medicinals of the period consisted of crude materials. A "pure" drug was one uncontaminated by parts of other plants or extraneous matter; shelf life was not considered, even though some medicinals were transported over great distances. Further, apothecaries were known to hide substitutions in complex medications. Identification of specific herbs could easily be confused because of local names and translation through several languages. If the prescribed material was not available, one deemed to be equivalent might be substituted. Some simply engaged in fraudulent substitution [24, 25]. Though a modern definition of purity and that of the Middle Ages are vastly different, Peter clearly recognized its importance.

2. The patient should have the disease for which the medicinal is intended. Diagnosis depended upon signs and symptoms alone. For example, an ulcer of the cornea was not distinguished from an ulcerating cancer of the eyelid [26]. Problems of abdominal pain were diagnosed according to location and associated vomiting or diarrhea. In this setting, medicinals used with illnesses now known to be self-limited might be deemed highly efficacious. These limitations not withstanding, here also Peter defined an important principle of therapeutics.

3. The medicine should be given alone. This was an era of complex polypharmacy. Several plants might be dried and powdered and mixed with the bile of several kinds of birds, and a dung or two, all heated together and then used as a curative for a number of ailments. Peter recognized that the efficacy of one could not be separated from the many used together. In this rule, Peter comments on confusion arising from deliberate simultaneous use of more than one active principal.

4. The medicine should be the opposite of the disease. Since the time of Empedocles (ca. 500 BC), amplified by Hippocrates and Galen, Greek humoral philosophy held that all natural objects are composed of four qualities: hot, cold, dry, and moist. Animals, including man, expressed those qualities in four humors: blood, phlegm, yellow bile, and black bile. It was understood that health was characterized by a natural balance (eucrasia) of the qualities and humors, and that disease occurred with imbalance (dyscrasia). Blood was deemed to be hot and moist; phlegm cold and moist; yellow bile, hot and dry; and black, cold and dry. It was expected that medicinals would have their beneficial effect through restoring balance by removing excesses of the offending humor. Medicinals were known for their specific hot or cold, moist or dry properties, not to be confused with the "accident" of administration in a hot, cold, moist, or dry form. To be effective, they should oppose the excess to be treated. Using the knowledge of the times, these were creative and rational solutions...

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