Cathcart’s *ether spray microtome* (fig. 4).--This, or its more recent modifications (_see_ later), is perhaps the most useful and economical microtome for the purposes of the student. Its prime cost is low, it is small and portable as well as being clean and inexpensive to work with. It consists of an oak frame which can be firmly clamped on to a table. On this frame are two narrow parallel supports about two inches high, which are covered by strips of plate glass, and serve as smooth rests along which the razor may glide in making sections. Between them is a brass well and in this a zinc plate firmly fixed in the horizontal position, which is almost at the level of the glass runners. It is capable of being raised or lowered through about 3/8 inch by means of a screw with a very fine and accurate thread. This screw is turned by a large milled wheel beneath the microtome. Just beneath the zinc plate are two small tubes, one connected with an india-rubber bellows, the other with a bottle at the side which contains ether. As the air issues from the first tube, it passes over the open end of the second, and thus draws the ether out and makes it play on the zinc plate, and at the same time causes it rapidly to evaporate, and so reduces the temperature of the zinc plate. In cutting sections with this microtome the tissue is taken out of the gum and placed on the zinc plate. The bellows are then worked until the gum on the zinc plate is completely frozen. The plate should be lowered by means of the screw until the surface of the piece of tissue is on a level with the glass runners. These and the razor should then be wetted with water. The razor being held firmly in the hand is pushed along the glass runners in a rather oblique direction. The plate should then be raised by turning the screw below through a very small arc, another section taken off and so on. Sections are carefully removed from the razor to a vessel of water by means of a soft wet camel’s hair brush. The needle should never be used for this purpose. If the specimen is very delicate, and likely to be spoiled by being curled up on the knife, the latter should be kept cold by frequently dipping it in a vessel containing lumps of ice in water. The gum will then remain frozen after cutting, and support the tissue better. Each section should be at once transferred to a glass slide from the knife, washing it off with a stream of ice water from a pipette. The knife that is used may be an ordinary razor, with the edge ground straight. It requires to be held steadily with both hands. As this is rather inconvenient, Dr. Sheridan Délépine suggested the employment of an ordinary plane iron such as is used in a carpenter’s plane. This only requires one hand, and the other can be kept on the head of the screw beneath to raise the plate at once after each stroke of the knife. Its disadvantages are that it is rather heavy for prolonged working, and that it is less easy to “set” than a razor.