HISTOLOGICAL METHODS. 189 



355. Turn-table. The dammar or white zinc cells 

 above mentioned are made with the aid of Shadbolt's turn- 

 table (Fig. 63), consisting of a 



rotary brass disc with a series of 

 concentric lines around its centre. 

 There are clips for fixing a slide, 

 and a wooden board for support- 

 ing the whole. The slide is 

 centred and fixed by the clips. 

 A brush dipped in the varnish is 

 held over one of the rings, and 

 the table turned rapidly. The 



apparatus is also used for putting a ring of varnish round 

 the margin of the cover-glass in sealing up a preparation. - 



356. The spreading out of Sections. In dealing 

 with large sections or with membranes there is often consi- 

 derable difficulty in spreading them out. This difficulty 

 may, however, be readily overcome by floating them on to 

 the slide by the method described in 87. 



357. Mounting-clip. In the case of sections that can 

 bear some pressure, and which are difficult to keep perfectly 



flat, a mounting-clip may be ap- 

 plied until the cover-glass is 

 fixed by glycerine jelly, dam- 

 mar, or some cement (Fig. 64). 

 It consists of a brass wire 

 bent so as to form a spring. 

 The end that is applied to the 

 FIG. 64.-Mounting-ciip. COV er-glass is covered with 



leather. In the case of bone, tooth, or cartilage, it may be 

 used, but the section is apt to be spoilt unless the spring 

 be feeble, and, indeed, in most cases no such thing need be 

 used. 



358. Cements. When the object is mounted in 

 Canada balsam or dammar, no cement is required ; but if 

 any other preservative substance be employed, even glycerine 

 jelly for it is hygroscopic the margin of the cover-glass 

 must be varnished. Dry the slide with bibulous paper, 

 then paint on a layer of gold-size, allow it to dry, and lastly 



