The record of Cardan's life for the next two years is a meagre one. His rest was constantly disturbed either by the machinations of his foes or by the dread thereof, the evil last-named being probably the more noxious of the two. As long ago as 1557 he had begun the treatise _De Utilitate ex Adversis Capienda_, a work giving evidence of careful construction, and one which, as a literary performance, takes the first rank.[200] This book had been put aside, either through pressure of other work or family troubles, but now the circumstances in which he found himself seemed perfectly congenial for the elaboration of a subject of this nature, so he set to work to finish it, concluding with the chapter _De Luctu_, which has been used largely as the authority for the foregoing narrative of Gian Battista's crime and death. At this period, when his mind was fully stored and his faculties adequately disciplined for the production of the best work, he seems to have realized with sharp regret that the time before him was so short, and that whatever fresh fruit of knowledge he might put forth would prove of very slight profit to him, as author. Writing of his replies given to certain mathematical professors, who had sent him problems for solution, he remarks that, although he may have a happy knack of dispatching with rapidity any work begun, he always begins too late. In his fifty-eighth year he answered one of these queries, involving three very difficult problems, within seven days; a feat which he judges to be a marvel: but what profit will it bring him now? If he had written this treatise when he was thirty he would straightway have risen to fame and fortune, in spite of his poverty, his rivals, and his enemies. Then, in ten years' space, he would have finished and brought out all those books which were now lying unfinished around him in his old age; and moreover would have won so great gain and glory, that no farther good fortune would have remained for him to ask for. Another work which he had begun about the same time (1558) was the treatise on _Dialectic_, illustrated by geometrical problems and theorems, and likewise by the well-known logical catch lines _Barbara Celarent_. During the summer vacation of 1561 he returned to Milan, and began a _Commentary on the Anatomy of Mundinus_, the recognized text-book of the schools up to the appearance of Vesalius. In the preface to this work he puts forward a vigorous plea for the extended use of anatomy in reaching a diagnosis.[201] He had likewise on hand the _Theonoston_, a set of essays on Moral subjects written something in the spirit of Seneca; and, after Gian Battista's death, he wrote the dialogue _Tetim, seu de Humanis Consiliis_. In the year following, 1561, a farther sorrow and trouble came upon him by the death of the English youth, William. If he was guilty of neglect in the case of this young man--and by his own confession he was--he was certainly profoundly grieved at his death.