Notwithstanding his devotion to his practice, Auenbrugger did not cease to make observations that occasionally he considered worthy of being committed to paper. He was especially careful in the study of his cases, and left fully written records of over 400 important cases that he had studied very faithfully. His attention seems to have been attracted particularly to certain mental diseases. This work was done half a century before even the first beginnings of the modern classifications of mental diseases were attempted. He wrote a short article with regard to mania and its treatment, and a longer article on melancholia. How well he recognized the essential feature of this latter affection and the main symptom that must be guarded against, can be gathered very well from the title of his paper, which he called "The Still Madness, or the Impulse to Self-Murder." It is about the time that he was engaged in the study of melancholia, perhaps as a contrast to sadder things, that he wrote a comic opera, of which we shall have more to say presently. His description of the conditions that he saw during an epidemic of dysentery that occurred in Vienna show how exact and careful a clinical observer he could be, and that the demands of his practice did not absorb all his attention to the detriment of his faculty for observation. He seems himself to have suffered from a severe attack of typhus fever which raged epidemically in Vienna in 1798. Auenbrugger had a wide circle of interests beyond the subject of medicine. There is a family tradition that he had a magnificent library. He seems with true Viennese spirit to have been a great devotee of the opera, and to have had an especial liking for music. He wrote the text, {80} score, and libretto of a comic opera with the title, "The Chimney Sweep." This operetta evidently enjoyed more than a _succes d'estime_, and further writing in this line was confidently expected from him by his friends. There is even a story to the effect that the Empress Maria Theresa, of whom he was an intimate friend, and who made use, it is said, of his counsel in political matters more than once, asked him why he did not follow up his first success in operatic writing. His blunt reply shows how intimate must have been his relations with the great empress. He said he had things much better with which to occupy himself than the writing of comic operas.