E. L. was a man about seventy-eight years of age; had been admitted on the incurable establishment January 3, 1767. By report, I have understood that he was formerly in the navy, and that his insanity was caused by a disappointment of some promotion which he expected. It was also said that he was troublesome to some persons high in office, which rendered it necessary that he should be confined. At one time he imagined himself to be the king, and insisted on his crown. During the time I had an opportunity of knowing him, he conducted himself in a very gentlemanly manner. His disposition was remarkably placid, and I never remember him to have uttered an unkind or hasty expression. With the other patients he seldom held any conversation. His chief amusement was in reading, and writing letters to the people of the house. Of his books he was by no means choice; he appeared to derive as much amusement from an old catalogue as from the most entertaining performance. His writings always contained directions for his release from confinement; and he never omitted his high titles of God's King, Holy Ghost, Admiral and Physician. He died June 13, 1797, worn out with age. He was opened two days after death. The scull was thick and porous. There was a large quantity of water between the different membranes. The membrana arachnoidea was particularly opake: the veins seemed to contain air: in the medullary substance the vessels were very copious and much enlarged: the lateral ventricles contained two ounces of pellucid water: the consistence of the brain was natural. It has been stated by a gentleman of great accuracy, and whose situation affords him abundant opportunity of acquiring a knowledge of diseased appearances, that the fluid of hydrocephalus appears to be of the same nature with the water which is found in dropsy of the thorax and abdomen[3]. That this is generally the case, there can be no doubt, from the respectable testimony of the author of the Morbid Anatomy. But in three instances, where I submitted this fluid to experiment, it was incoagulable by acids and by heat: in all of them its consistence was not altered even by boiling. There was, however, a cloudiness produced; and after the liquor had stood some time, a slight deposition took place of animal matter, which, prior to the application of heat or mineral acids, had been dissolved in the fluid. This liquor tinged green the vegetable blues: produced a copious deposition with nitrat of silver, and on evaporation afforded cubic crystals (nitrat of soda). From this examination it was inferred, that the water of the brain, collected in maniacal cases, contained a quantity of uncombined alkali and some common salt. What other substances may enter into its composition, from want of sufficient opportunity, I have not been enabled to determine. CASE XXIV.