Jerome Cardan believed that he composed books while asleep, and his case is often adduced as an example of the height to which the imagination can attain during sleep. But this great man was superstitious to an extreme degree; he believed that he had a familiar spirit, from whom he received intelligence, warnings, and ideas, and asserted that when awake he frequently saw long processions of men, women, animals, trees, castles, instruments of various kinds and many figures, different from anything in this world. His evidence relative to his compositions and mathematical labors when asleep is not therefore of a trustworthy character. As regards the memory in sleep, it is undoubtedly exercised to a considerable extent. In fact, whatever degree of activity the mind may then exhibit is based upon events the recollection of which has been retained. But there is more or less error mingled with a small amount of truth. The unbridled imagination of the sleeper so distorts the simplest circumstances as to render their recognition a matter of no small difficulty, and thus it scarcely if ever happens that events are reproduced during sleep exactly as they occurred or as they would be recalled by the mind of the individual when awake. Frequently, also, recent events which have made a strong impression on our minds are forgotten, as when we dream of seeing and conversing with persons not long dead. And yet it has sometimes happened that incidents or knowledge which had long been overlooked or forgotten, or which could not be remembered by any effort during wakefulness have been strongly depicted during sleep. Thus Lord Monboddo[43] states that the Countess de Laval, a woman of perfect veracity and good sense, when ill, spoke during sleep in a language which none of her attendants understood, and which even she was disposed to regard as gibberish. A nurse detected the dialect of Brittany; her mistress had spent her childhood in that province, but had lost all recollection of the Breton tongue, and could not understand a word of what she said in her dreams. Her utterances applied, however, exclusively to the experience of childhood, and were infantile in structure. Abercrombie[44] relates the case of a gentleman who was very fond of the Greek language, and who, in his youth, had made considerable progress in it. Subsequently being engaged in other pursuits, he so entirely forgot it that he could not even read the words; often, however, in his dreams he read Greek works, which he had been accustomed to use at college, and had a most vivid impression of fully understanding them. Many other instances of the action of memory during sleep might be brought forward, but the subject will be more appropriately considered in the chapter on dreams.