When the microscope was first invented, it was regarded as a mere accessory, a plaything, an unnecessary addition, and an imposition upon the medical profession and upon the public in general. But since 1840, when the European oculists and scientists began to make microscopical researches and investigations, not only in the medical profession, but also in botanical and geological studies, etc., and since 1870, when, throughout the civilized world, the microscope came into general use in chemical analysis and other studies, it ceased to be considered an accessory, and is now regarded as an extremely necessary apparatus, especially in minute examinations and investigations; also in the advancement of every branch of science and art. Had Galen, Celsus, Hippocrates, and the other great scientists of old, known the use of the microscope, they would have made no such grave blunders as in the advocation of the theory that the arteries of the human body contain and carry air during life, instead of oxygenized blood only. They were of the erroneous opinion that the blood stayed in the extremities, not to nourish and sustain the tissues, but simply to act as a humor in lubricating the same (tissues). Then, again, had it not been for the microscope, the great English surgeon and physician, James Paget, would not have discovered that deadly parasite, the trichina-spiralis, which had already slaughtered thousands upon thousands of human beings. And yet the existence of trichina-spiralis may be dated as far back as the time of Moses, who even then advocated prohibition of the use of pork as a food, and who considered pork not only an unwholesome food, but dangerous and even poisonous. The microscope is certainly the best friend that a scientist can have. A physician without a microscope is like a man without eyes: he is uncertain and unprotected and must be considered incompetent, simply because he cannot arrive at a correct and positive conclusion in diagnosing and prognosing his case. The value of the microscope cannot be overestimated, at least in the examination of the sputa of a human being, and thus being able to state positively whether or not the man is suffering from consumption (Tuberculosis). How important it is to be able to state with certainty at an early date whether or not the patient is suffering from cancer of the stomach, by examining the vomits microscopically. The microscope is composed of a simply constructed horse-shoe or tripod base with a column, tube, reflector, and lenses of different magnifying powers, ranging from one to five thousand diameters. It is a most extraordinary and at the same time a most simple apparatus, an invaluable instrument, whose use any person with a little skill can learn in a few hours' practice.