HISTOLOGICAL METHODS. 15 x 



below, and the tube of the microscope above. This chamber is con- 

 venient enough for low, but not for high powers ; and in any case the 

 air in the chamber tends to become dry. This difficulty, together with 

 that experienced in using a moist chamber with very high powers, 

 such as the ^ objective, has been entirely overcome by Mr. Dallinger 

 and Dr. Drysdale. 



271. Dallinger and Drysdatts Moist Chamber. This 

 apparatus (Monthly Microscop. Journ., vol. xi. p. 97), con- 

 sists of a plate of glass about a tenth of an inch thick, 

 and of a size suitable for the stage of the microscope, room 

 for its movement in all directions being allowed. (A, Fig. 



FIG. 53. Dallinger and Drysdale's moist chamber. A, Glass stage. B, Glass cell 

 with caoutchouc membrane. C, Vertical section of stage and cell, with lens, a 



53). At one side of the glass plate (a) there is a rectangular 

 arm, to which a brass plate (b) with a ring is fixed. The 

 latter holds an ordinary beaker with water. The glass 

 plate being too thick for the illumination of an object with 

 a powerful achromatic condenser, a piece is cut out of its 

 centre, and thin glass cemented over the aperture (e in A 

 and in C). Moisture is continually supplied by a strip of 

 thin calico (/) spread over the plate and dipping into the 

 water in the beaker. An aperture must be made in its 

 centre about two or three times the breadth of the cover- 

 glass (g) employed. The inventors found an aperture | 

 inch for a cover-glass of inch work well. A thin piece of 

 caoutchouc, with an aperture in its centre, is tied over 

 a glass cylinder (B) about i J inch in diam. and inch in 



