Simples knowable only from experience.
It is perhaps in his work on medicinal simples that Galen lays most stress upon the importance of experience. Indeed he sees no other way to learn the properties of natural objects than through the experience of the senses.[705] “For by the gods,” he exclaims, “how is it that we know that fire is hot? Are we taught it by some syllogism or persuaded of it by some demonstration? And how do we learn that ice is cold except from the senses?”[706] And Galen sees no advantage in spending further time in arguments and hair-splitting where one can learn the truth at once from the senses. This thought he keeps repeating through the treatise, saying, for example, “The surest judge of all will be experience alone, and those who abandon it and reason on any other basis not only are deceived but destroy the value of the treatise.”[707] Moreover, he restricts his account of medicinal simples to those with which he is personally acquainted. In the three books treating of plants he does not mention all those found in all parts of the world, but only as many as it has been his privilege to know by experience.[708] He proposes to follow the same rule in the ensuing discussion of animals and to say nothing of virtues which he has not tested or of substances mentioned in the writings of past physicians but unknown to him. He dares not trust their statements when he reflects how some have lied in such matters. In the middle ages Albertus Magnus talks in much the same strain in his works on animals, plants, and minerals, and perhaps he was stimulated to such ideals, consciously or unconsciously, directly by reading Galen or indirectly through Arabic works, by Galen’s earlier expression of them. Galen mentions some virtues ascribed to substances which he has tested by experience and found false, such as the medicinal properties attributed to the belly of a seagull[709] and some of those claimed for the marine animal called torpedo.[710] Anointing the place with frog’s blood or dog’s milk will not prevent eyebrows that have been plucked out from growing again, nor will bat’s blood and viper’s fat remove hair from the arm-pits.[711] Also the brain of a hare is only fairly good for boys’ teeth.[712]
Experience and food science.
In beginning his work on food values[713] Galen states that many have discussed the properties of aliments, some on the basis of reason alone, some on the basis of experience alone, but that their statements do not agree. On the whole, since reasoning is not easy for everyone, requiring natural sagacity and training from childhood, he thinks it better to start from experience, especially since not a few physicians are of the opinion that only thus can the properties of foods be learned.
Experience and compounds.
The Empirics contended that most compound medicines had been hit upon by chance, and Galen grants that the Dogmatics usually are unable to give reasons for the ingredients of their doses and find difficulty in reproducing a lost prescription.[714] But he holds that reasons can be given for the constituents of the compound and that the logical discovery of such remedies differs from the empirical.[715] His own method was to learn the nature of each disease and the varied properties of simples, and then prepare a compound suited to the disease and to the patient.[716] On the other hand, we see how much depends upon experience from his confession that sometimes he has hastily prepared a compound from a few simples, sometimes from more, sometimes from a great variety. If the compound worked well, he would continue to use it, sometimes making it stronger and sometimes weaker.[717] For as you cannot put together compounds without rational method, so you cannot tell their strength certainly and accurately without experience.[718] He admits that no one can tell the exact quantity of each ingredient to employ without the aid of experience,[719] and says, “The proper proportions in the mixture we shall find conjecturally before experience, scientifically after experience.”[720] In these treatises upon compound medicines, unlike that on medicinal simples, Galen gives the prescriptions of former physicians as well as some tested by his own experience.[721] Sometimes, however, he expresses a preference for the medicines of those writers who were “most experienced”; and once says that he will give some compounds of the more recent writers, who in their turn had selected the best from older writers of long experience and added later discoveries.[722] We suspect, however, that some of these prescriptions had not been tested for centuries.
Suggestions of experimental method.
Galen gives a few directions how to regulate medical observation and experience, although they cannot be said to carry us very far on the road to modern laboratory research. He saw the value of “long experience,” a phrase which he often employs.[723] He states that one experience is enough to learn how to prepare a drug, but to learn to know the best medicines in each kind and in different places many experiences are required.[724] Medicinal simples should be frequently inspected, “since the knowledge of things perceived by the senses is strengthened by careful examination.”[725] Galen advises the student of medicine to study herbs, trees, and fruit as they grow, to find out when it is best to pluck them, how to preserve them, and so on. But elsewhere he states that it is possible to estimate the general virtue of the simple from one or two experiences.[726] However, he suggests that their effect be noted in the three cases of a perfectly healthy person, a slightly ailing patient, and a really sick man.[727] In the last case one should further note their varying effects as the disease is marked by any excess of heat, cold, dryness, or moisture. Care should be taken that the simples themselves are pure and free from any admixture of a foreign substance.[728] “It is also essential to test the relation to the nature of the patient of all those things of which great use is made in the medical art.”[729] One condition to be observed in experimental investigation of critical days is to count no cases where any slip has been made by physician or patient or bystanders or where any other foreign factor has done harm.[730] Galen was acquainted with physical experiments in siphoning, for he says that, if one withdraws the air from a vessel containing sand and water, the sand will follow before the water, which is the heavier (sic?).[731]
Difficulty of medical experiment.
Galen also points out some of the difficulties of medical experimentation. One is the extreme unlikelihood of ever being able to observe in even two cases the same combination of symptoms and circumstances.[732] The other is the danger to the life of the patient from rash experimenting.[733] Thus Galen more than once tells us of abstaining from testing some remedy because he had others of whose effects he was surer.