When Galen again attacked Holland six years later he was in alliance with Louis, but he soon deserted his new friend, and fought for the emperor Leopold I.
Galen showed himself anxious to reform the church, but his chief energies were directed to increasing his power and prestige.
His work is not essentially different from that of his predecessors Rhazes and Ali; all present the doctrine of Galen, and through Galen the doctrine of Hippocrates, modified by the system of Aristotle.
Galen is said to have invented hiera-picra, which he employed as an anthelmintic; it is still used in England as a domestic remedy.
He wrote numerous translations, of Galen, Aristotle, Ilariri, IIunain ben Isaac and Maimonides, as well as several original works, a Sepher Anaq in imitation of Moses ben Ezra, and treatises on grammar and medicine (Rephuath geviyyah), but he is best known for his Talzkemoni, a diwan in the style of Ilariri's Magimat.