[Sidenote: Adverse criticism of past writers.] This critical employment of past authorities is frequently illustrated in Galen’s works. He mentions a great many names of past physicians and writers, thereby shedding some light upon the history of Greek medicine; but at times he criticizes his predecessors, not sparing even Empedocles and Aristotle. Although he cites Aristotle a great deal, he declares that it is not surprising that Aristotle made many errors in the anatomy of animals, since he thought that the heart in large animals had a third ventricle.[673] As we have already seen in discussing the topic of weights and measurements, Galen especially objects to the vagueness and inaccuracy of many past medical writers,[674] or praises individuals like Heras who give specific information.[675] He also shows a preference for writers who give first-hand information, commending Heraclides of Tarentum as a trustworthy man, if there ever was one, who set down only those things proved by his own experience.[676] Galen declares that one could spend a lifetime in reading the books that have already been written upon medicinal simples. He urges his readers, however, to abstain from Andreas and other liars of that stamp, and above all to eschew Pamphilus who never saw even in a dream the herbs which he describes. [Sidenote: Galen’s estimate of Dioscorides.] Of all previous writers upon _materia medica_ Galen preferred Dioscorides. He writes, “But Anazarbensis Dioscorides in five books discussed all useful material not only of herbs but of trees and fruits and juices and liquors, treating besides both all metals and the parts of animals.”[677] Yet he does not hesitate to criticize certain statements of Dioscorides, such as the story of mixing goat’s blood with the _terra sigillata_ of Lemnos. Dioscorides had also attributed marvelous virtues to the stone Gagates which he said came from a river of that name in Lycia; Galen’s comment is that he has skirted the entire coast of Lycia in a small boat and found no such stream.[678] He also wonders that Dioscorides described butter as made of the milk of sheep and goats, and correctly states that “this drug” is made from cows’ milk.[679] Galen does not mention its use as a food in his work on medicinal simples, and in his treatise upon food values he alludes to butter rather incidentally in the chapter on milk, stating that it is a fatty substance and easily recognized by tasting it, that it has many of the properties of oil, and in cold countries is sometimes used in baths in place of oil.[680] Galen further criticizes Dioscorides for his unfamiliarity with the Greek language and consequent failure to grasp the significance of many Greek names. [Sidenote: Galen’s dogmatism: logic and experience.]