“Medicine is a science from which one learns the conditions of the human body with regard to health and the absence of health, the aim being to protect health when it exists and restore it when absent. Someone might say to us that medicine is divided into theoretical and practical parts and that, by calling it a science, we have considered it as being all theoretical. To this we respond by saying that some arts and philosophy have theoretical and practical parts, and medicine, too, has its theoretical and practical parts. The division into theoretical and practical parts differs from case to case, but we need not discuss these divisions in disciplines other than medicine. If it is said that some parts of medicine are theoretical and other parts are practical, this does not mean that one part teaches medicine and the other puts it into practice – as many researchers in this subject believe. One should be aware that the intention is something else: it is that both parts of medicine are science, but one part is the science dealing with the principles of medicine, and the other with how to put those principles into practice”.
“You can tell the potency of drugs in two ways, by analogy (qiyas) and by experiment (tajribah). We say experimenting leads to knowledge of the potency of a medicine with certainty after taking into consideration certain conditions.”
“The drug must be free from any acquired quality: this can occur if the drug is exposed to temporary heat or cold, if there is a change in the essence of the drug, or if the drug is in close proximity to another substance. Water, although cold by nature, will give warmth as long as it is heated; euphorbium, although hot by nature, will have a cold effect when cold; almond, although naturally neutral, will have a strong effect of heat if it turns rancid; and fish, although cold, is a strong source of heat if salt is added to it.
“The experiment must be done on a single, not a composite, condition. In the latter case, if the condition consists of two opposite diseases and the drug is tried and found beneficial in both, we cannot infer the real cause of the cure. Example: if we treat a patient suffering from phlegm fever with agaric and the fever abates, this does not mean that because it was useful for a hot illness agaric possesses the property of coldness. It is possible that the drug was effective because it dissolved the phlegm or removed it; when the [phlegm] disappeared the fever disappeared. This action represents both the direct and the accidental benefit of the drug. The direct benefit relates to the [phlegm], and the indirect refers to the fever.
“The drug must be tested on two contrary conditions. If it is effective on both, we cannot judge which condition benefited directly from the drug. It is possible that the drug acted directly against one disease, and acted against the symptom of the other. Scammony, if used to treat a cold disease, would no doubt have a warming effect and bring benefit. If we try it on a hot disease, such as diurnal fever, it would also have a beneficial effect because it gets rid of yellow bile. In these cases, an experiment would be of no help in deciding whether [the drug] is hot or cold, unless we could know that it acted directly on one disease and acted on a symptom of the other.
“The potency of the drug should be equal to the strength of the disease. If some of the drugs are inadequate with regard to heat when compared to the coldness of an illness, they will not be able to effect a cure. Sometimes during their application against coldness, their function for producing warmth is weakened. So it is best to experiment first using the weakest [dosage] and then increase it gradually until you know the potency of the drug, leaving no room for doubt.
“One should consider the time needed for the drug to take effect. If the drug has an immediate effect, this shows that it has acted against the disease itself. If its initial effect is contrary to what comes later, or if there is no initial effect at first and the effect shows up later, this leads to uncertainty and confusion. Actions in such cases could be accidental: their effect is hidden at first and later comes into the open. The confusion and uncertainty relate to the potency of the drug.
“The effect of the drug should be the same in all cases or, at least, in most. If that is not the case, the effect is then accidental, because things that occur naturally are always or mostly consistent.
“Experiments should be carried out on the human body. If the experiment is carried out on the bodies of [other animals] it is possible that it might fail for two reasons: the medicine might be hot compared to the human body and be cold compared to the lion’s body or the horse’s body… The second reason is that the quality of the medicine might mean that it would affect the human body differently from the animal body…
“These are the rules that must be observed in finding out the potency of medicines through experimentation. Take note!” (page 116)
The editors are grateful to:
Dr Safaa Al-Essa FRCPEdin for identifying in the College’s copy of Ibn Sina’s Qanun the passages reproduced here.
The Wellcome Trust for making available the portrait of Ibn Sīnā (c.980-c.1037 CE).