An introductory chapter on the general subject of the character of poisonous matters, illustrated by some gruesome and Munchausen-like tales, borrowed mainly from Avicenna and Ruffus, on the wonders of acquired immunity to poisons, the horrors of the basilisk, the _armaria_ (_?_), the deaf adder (_aspis surda_) and the red-hot _regulus_ of Nubia, leads naturally to the consideration of some special poisons derived from the three kingdoms of nature. Very characteristically Gilbert displays his caution in the discussion of a dangerous subject by the following preface: _Abstineamus a venesis occultis quae non sunt manifesta, ne virus in angues adjiciamus, aut doctrinam perniciosam tradere videamur_ (f. 351 a). Beginning then with metallic mercury (_argentum vivum_), he considers the poisonous effects of various salts of lead and copper, the vegetable poisons hellebore, anacardium (_anacardis?_), castoreum, opium and cassilago (_semina hyoscyami_), and then proceeds to the bites or rabid men and animals, hydrophobia, and the bites of scorpions, serpents and the _animalia annulosa_, that is, worms, wasps, bees, ants and spiders. Space does not permit a careful review of this interesting subject, but a novel form of poisoning by the use of quicksilver is startling enough to claim our attention. Gilbert tells us that pouring metallic mercury into the ear produces the most distressing symptoms, severe pain, delirium, convulsions, epilepsy, apoplexy and, if the metal penetrates to the brain, ultimate death. In the treatment of this condition certain physicians had recommended the insertion into the ear of a thin lamina of lead, upon which it was believed that the mercury would fasten itself and might thus be drawn out. Avicenna objected to this that the mercury was liable to speedily pass into the ear so deeply as to be beyond the reach of the lead. Gilbert suggests as an improvement of the treatment that a thin lamina of gold be substituted for the lead, "because mercury thirsts after gold as animals do after water, as it is held in the books on alchemy" (_in libris allzinimicis_). This fact, too, he tells us can be easily demonstrated externally by placing upon a plate a portion of gold, and near, but not in contact with it, a little quicksilver, when the silver, he says, will at once "leap" upon the gold. Avicenna suggests that the patient stand upon the foot of the side affected, lean his head over to the same side, steady it in that position with the hands, and then leap suddenly over upon the other foot--demonstrating thereby his knowledge of both gravity and inertia. Manifestly our "laboratory physicians" of the present day can assume no airs of priority! The Compendium closes with two very sensible chapters on the hygiene of travel, entitled "_De regimine iter agentium_" and "_De regimine transfretantium_."