Cites Caldwell Automatic Microtome
Description:

'Mr. W.H. Caldwell's very novel and ingenious instrument has effected a revolution in the art of section-cutting, especially where it is desired to cut a very large number of sections of equal thickness in a very short time, and to insure teir arrangement in their proper consecutive order and with the same side upwards. It may easily be made to deliver in one continuous ribbon sections at a rate of 100 per minute, and when driven by means of a motor, such as the water-motor used for it at Cambridge, more than double this number can be obtained.

The general form of this instrument, which is supported on a heavy iron frame 36 in. long, 8 in, wide, and 11 in. high, resting on four feet, is shown in fig. 29, the object-holder with its carrier (in enlarged view) at fig. 30, and the top plate of the microtome, with object, knife, and belt, at fig. 31.

The carrier, with the object, moves backward and forwards beneath the razor (any ordinary razor does), which remains stationary in the clamp in which it is fixed (figs. 29 and 31). The carrier is pulled forwards by the action of a roller fixed eccentrically to the axis of the large fly-wheel, and connected with it by the link and cords shown in fig. 29. It is drawn back again by the strong spring shown on the left. The extent of its motions is regulated so that the surface of the imbedding mass just clears the razor when the carrier is at its maximum and minimum distance from either end of the frame.

The cylindrical vessel which holds the imbedding mass and object is slipped into a tube or socket, in a cross-piece attached to two quadrants, arranged so that the socket may be set at any angle desired, and clamped by the vertical screw underneath (see fig. 30). This arrangement is for use when the object has not been symetrically imbedded. For a rough adjustment of the object to the level of the knife the socket can be slipped up or down in the cross-piece. For more accurate, yet still rapid, adjustment the entire object-holder may be raised and lowered by the large micrometer screw. To this screw is attached a ratchet wheel with clicks, which are controlled by the lower, horizontal screw (fig. 30), and by means of which the object is raised automatically. When the clicks engage half a tooth the sections will be 2.5 µ (or 1/10,000 in.) in thickness, a whole tooth 5 µ, and so on.

The great novelty of the instrument, however, consists in the use of an endless band, 2 in. wide, to receive the sections as they come from the razor. With proper imbedding material the sections will adhere to one another and come off the razor in the form of a ribbon, and as soon as a sufficient length has been cut the end is picked up by a needle or scalpel and placed on the band which is just above the razor (see fig. 31). By the arrangement of cords and rods, shown in fig. 29, the band is adjusted so that at each "throw" of the object-carrier (or turn of the fly-wheel) it is moved forwards through a distance equal to the breadth of the surface which is being cut. The ribbon consequently travels up the band until the top is reached, when the sections can be cut off in convenient lengths for mounting.

The directions for using the instrument issued by its manufacturers, the Cambridge Scientific Instrument Co., have been re-published, [note: 'Quart. Journ. Micr. Sci., xxiv. (1884) pp. 648-54.'] and need not be repeated here. The most important points insisted upon are the sharpness of the razor and the accurate parallelism of the sides of the imbedding material from which the sections are cut, so that the ribbon of sections may be quite straight for convenient mounting. The Company supply special imbedding material, so that sections may be satisfactorily cut within a very considerable range of temperature, obviating the necessity of exactly adjusting the temperature of the room to the specimen of paraffin in use, or, as an alternative, of providing a number of specimens of paraffin with different melting points.

The ordinary 3 X 1 slides are not of course large enough for the ribbons, and slides of double the size (6 in. X 2 in.) are found the most convenient, with cover-glasses 5 in. X 1 1/2 in. On such a slide five or six rows of the ribbons may be placed, each row containing from fifty to one hundred sections or more.' (150-153)