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Rh ''II. Fluid-Mantle Olfactometer.'' In this instrument, the constant saturation of the hollow porcelain cylinder is secured in the following manner: A section of wide glass tubing is secured between two circular and cork-lined end-plates of metal. One of the metal plates,—that which when the instrument is adjusted is nearer to the subject,—is furnished with three equidistant rods, inside of which the disks of cork and the glass tube fit. The three rods terminate in three screws with detachable heads. The screws pass through holes in the other metal plate, The plates are bored at the center to circular openenings, 8 mm. in diameter, which coincide with the bore of the enclosed porcelain cylinder. The clyinder itself, which has exactly the length of the glass tube,—10 cm.,—is held in place simply by the pressure of the end-plates. The glass inhaling-tube passes through the screen into the bore of the cylinder. The odorous solution is put into the space between the cylinder and the glass tube with a pipette through one of two holes, 2 mm. in diameter, which are left one in each of tie two metal plates, and closed with cork-lined screw-heads. It would be better if there were two of these holes in each plate, for it is extremely difficult to force a sluggish liquid, such as glycerine, against the pressure of the air into the space around the cylinder. If the rubber of the pipette is flaccid, it becomes almost impossible.

The “shells” thus constructed for mantling the cylinder with liquid, are mounted in a horizontal position on a wooden table,—27.7 cm. long by 16.4 cm. wide,—which can be adjusted to the required height above a heavily leaded base. Each of the shells can be moved to and from the observer along a way of hard wood. The rack and pinion movement is governed by milled heads,—diameter 23 cm., —projecting from the table o right and left within easy grasp of the subject’s hand. A scale and pointer enable the observer to determine bow far the cylinder is moved.

The inhaling-tubes are made with the same bore and of glass of the same thickness as the graduated tubes used with the standard olfactometer, Those sent from Holland turn, one to the right and the other to the left before curving upward to be inserted in the nose, The metal sleeves, within which the tubes are cemented, do not bolt into the holes in the screen, but flare off each on its outer side into flat fan-shaped pieces of metal, which are screwed to tally with a mark on the screen. We made no experiments with these tubes, but used instead tubes of the same bore and thickness of glass, either with a somewhat shorter upright, or with but one curve. The tubes with one curve are precisely like the inhaling-tubes of the standard olfactometer, except that the part which extends through the screen is longer and is not graduated. It is a mistake to use two-jointed tubes at all, unless both nostrils are to be used, as in compensation-experiments. The extra curve seems to make no difference in the results, but it makes the tubes much harder to clean. The total length of our two-jointed tubes was $18 1/2$ cm., and that of our one-jointed tubes, $17 1/2$ cm. 11.3 cm. of every tube used must project beyond the screen. We fitted our tubes into hollow plugs of cherry wood turned to order in the shape of corks, so as to pass easily into the holes of the screen, and