Tobold's lamp consists of a brass tube containing several lenses, which are placed, one before the other, at such distances as to give the greatest possible amount of concentration of light. The back part of the tube is closed, while near the end two large holes are cut in its sides opposite to each other, through which the chimney of the lamp projects. The whole is fastened by means of clamps to a stand, to which is also attached a jointed arm bearing the reflector. This apparatus is used either in connection with a student's lamp or with an argand gas-lamp, and it will be found very convenient to have it mounted upon a gas-bracket which can be raised and lowered and swung from side to side. Mackenzie's light concentrator consists of a cylinder of sheet iron about 6 inches long by 2½ in diameter. Near one end a hole is cut in the side of the cylinder, and a short piece of tube holding a condensing lens is attached to the edge of the hole. This lens, which is plano-convex with a spherical curve, and of 2½ inches diameter, is placed with the plane side toward the light. {24} This concentrator is intended to be slipped over the chimney of an argand burner, and should be so adjusted that the centre of the flame corresponds with the centre of the lens. It may, however, be used in connection with a student's lamp, incandescent electric lamp, or even a candle, giving in all cases a very satisfactory light, which, however, must be reflected from the head mirror into the patient's mouth. The best light, however, when the examinations are conducted in the office of the physician, is the electric incandescent light, which presents numerous advantages over the gas or oil lamp. It is more brilliant and whiter than any other suitable artificial light, giving off neither gases nor heat, nor does it consume the oxygen in the room; and since the introduction and perfection of storage batteries it has become available and convenient for use in private houses. Numerous experiments which the author has carried on for some time have resulted in the application of this form of light for laryngoscopy in two ways which are both very satisfactory. The incandescent lamp is mounted upon the universal gas-bracket in place of the argand burner, and either the Tobold lamp or Mackenzie's light concentrator is slipped over it, so that it comes opposite the centre of the lens. In fact, the electric lamp is substituted for the gas-burner, and the whole apparatus is used as described above. The arc light may also be used in the same manner, but does not give as satisfactory results on account of its unsteadiness. [Illustration: FIG. 3. The Author's Electric Illuminator for the Laryngoscope.]