Cathcart’s Freezing Microtome.—This is a convenient and useful microtome for freezing purposes. Since its first introduction it has been much improved. The clamping arrangements give steadiness, and the principal screw is more effective; the freezing-plate is circular, and the arrangements made for preventing the ether from reaching the upper plate secures the object in view. This instrument can now be used for embedding as well as freezing. The directions for freezing are as follows:—
1. Place a few drops of mucilage (one part gum to three parts water) on the zinc plate.
2. Take a piece of the tissue to be cut, of about a quarter of an inch in thickness, and press it into the gum.
3. Fill the ether bottle with anhydrous methylated ether, and push the spray points into their socket. All spirit must of course have been previously removed by soaking for a night in water. The tissue should afterwards be soaked in gum for a like time before being cut.
Work the spray bellows briskly until the gum begins to freeze; after this work more gently. Be always careful to brush off the frozen vapour which, in a moist atmosphere, may collect below the zinc plate. If the ether should tend to collect in drops below the plate, work the bellows slower.
5. Raise the tissue by turning the milled head, and cut by sliding the knife along the glass plates.
6. After use, be careful to wipe the whole instrument clean.
7. Should the ether point become choked, clear by means of the fine wire provided for the purpose.
8. The instrument is intended for use with methylated sulphuric ether.
9. In clamping the instrument to a table, or other support, care should be taken that the zinc plate is in a horizontal position. If the plate be not horizontal, the gum will tend to run to one side.