The physiologist used to be like a man wishful to study the life of a city, and only able to do this by looking down from a terrace at the coming and going of the crowd, the perpetual stream of people in the street. Only of late years have we succeeded in penetrating into the houses by the roof, in spying out the inner life of each family, in studying the irrigation of the organs by the blood while they are at work or in repose. The pulse in the finest branches of the vessels and in the inward recesses of the organs is such a subtile, delicate phenomenon that we need the assistance of special instruments to intensify it before we can study it. I shall not do as many naturalists do, who think they should conceal the artistic side of their investigations from the fear of desecrating science. I know that every experimental work possesses an interesting side, which is quite lost owing to the aridity and severity with which scientific treatises are written, and I therefore abandon myself to the recollections of my investigations, careless of following the style of popular scientific books. II The first work which I published upon the circulation of blood in the human brain brings sad recollections to me. It was in June 1875 that my friend, Professor Carlo Giacomini, invited me to visit one of his patients in the syphilitic ward. It was a peasant woman, thirty-seven years of age, who, after having borne six children, had been infected by her husband with the most terrible disease to which a mother may fall a victim. For nine years the deadly poison had raged in her bones, and, with only short intervals of respite, had corroded a great part of the skeleton and destroyed the upper part of the skull from the nasal bones to the occiput. Medical art had proved powerless to arrest the disease. When Professor Giacomini took the woman out of pity into the hospital, her face was disfigured, her body was covered with sores and scars, the skin of the head was detached in various parts, the corroded skull had a blackish colour, like dead bones encased in living flesh. It was after hearing from this unhappy woman the story of her misfortune, and during the intense emotion which pity for her aroused, that I saw for the first time, through the fissures of the decayed bones, the movement of the uncovered brain. Even to-day, eight years later, when I think of that moment, a shiver runs over me as it did then.