BOOK VI. _THE AGE OF SCIENCE._ I. THE NINETEENTH CENTURY.—PHYSICAL SCIENCE ALLIED TO MEDICINE 443 Exit the Disease-demon.—Medical Systems again.—Homœopathy.—The Natural Sciences.—Chemistry, Electricity, Physiology, Anatomy, Medicine and Pathology.—Psychiatry.—Surgery.—Ophthalmology. II. MEDICAL REFORMS 464 Discovery of Anæsthetics.—Medical Literature.—Nursing Reform.—History of the Treatment of the Insane. III. THE GERM THEORY OF DISEASE 471 The Disease-demon reappears as a Germ.—Phagocytes.—Ptomaines.—Lister’s Antiseptic Surgery.—Sanitary Science or Hygiene.—Bacteriologists. —Faith Cures.—Experimental Physiology and the Latest System of Medicine. APPENDIX. ON SOME OF THE MORE IMPORTANT MINERALS USED IN MEDICINE 486 BOOK I. _THE MEDICINE OF PRIMITIVE MAN._ A POPULAR HISTORY OF MEDICINE. CHAPTER I. PRIMITIVE MAN A SAVAGE. The Medicine and Surgery of the Lower Animals.—Poisons and Animals.—Observation amongst Savages.—Man in the Glacial Period. There is abundant proof from natural history that the lower animals submit to medical and surgical treatment, and subject themselves in their necessities to appropriate treatment. Not only do they treat themselves when injured or ill, but they assist each other. Dogs and cats use various natural medicines, chiefly emetics and purgatives, in the shape of grasses and other plants. The fibrous-rooted wheat-grass, _Triticum caninum_, sometimes called dog’s-wheat, is eaten medicinally by dogs. Probably other species, such as _Agrostis caninia_, brown bent-grass, are used in like manner.[3] Mr. George Jesse describes another kind of “dog-grass,” _Cynosurus cristatus_, as a natural medicine, both emetic and purgative, which is resorted to by the canine species when suffering from indigestion and other disorders of the stomach. Every druggist’s apprentice knows how remarkably fond cats are of valerian root (_Valeriana officinalis_). This strong-smelling root acts on these animals as an intoxicant, and they roll over and over the plant with the wildest delight when brought into contact with it. Cats are extravagantly fond of cat-mint (_Nepeta cataria_). It has a powerful odour, like that of pennyroyal. There is no evidence, however, that these plants have any medicinal properties for which they are used by cats, they are merely enjoyed by them on account of their perfume. Dr. W. Lauder Lindsay, in his _Mind in the Lower Animals_, says that the Indian mongoose, poisoned by the snake which it attacks, uses the antidote to be found in the _Mimosa octandra_.[4]