ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



117 



cut from paraffin blocks, and should not be more than 2 /* in thickness. 

 Although mounted in direct apposition there was quite a distinct micro- 

 scopic interval between them, owing to the intervention of a thin layer 

 of the mounting medium ; and they were readily studied with ^. One 

 section was fixed to the slide, and the other to the cover-glass ; or in the 

 case of blood two cover-glasses were mounted in apposition, and then 

 mounted to the slide. By a composite block was meant a block com- 

 pounded of two ; a broad face of tissue was first exposed in each of the 

 two blocks, and the latter were then cemented together in paraffin ; 

 the sections were afterwards cut at right angles to the plane of apposition, 

 so that by placing the section with the line of junction across the field 

 of the microscope, a view was obtained of both the normal and abnormal 

 tissues at the same time. 



Hanging-Drop Preparations.*— J. R. Collins describes the following 

 simple contrivance for making a hanging-drop preparation. A small 

 rubber elastic band or washer of appropriate diameter and thickness is 

 smeared with vaseline upon one side. This side is then applied to the 

 slide. The upper surface of the band is now smeared with vaseline, and 

 the cover-glass with hanging-drop is applied to it. An air-tight cell is 

 thus readily made. This avoids the necessity for keeping special hollow- 

 ground slides, and is more convenient than the clumsy and troublesome 

 method of making a similar cell out of damped blotting-paper. 



By the use of rubber bands of different sizes the cells can be made 

 of any width and depth desired. Rings with a lumen of from 1-2 cm. 

 in diameter and of 2 mm. in thickness are very convenient. 



Ail-Metal 5 Cover-Glass Holder.f — E. Horcler has devised a cover- 

 glass holder (fig. 31) which has the following advantages : (1) it will 



Fig. 31. 



receive cover-glasses of any size in general use ; (2) being made entirely 

 of metal, it can be easily washed or sterilised ; (3) specimens requiring 

 heat can be placed in an oven with the films in position without fear of 

 ruining the holder. Directions for use : with the holder between finger 

 and thumb of left hand, pull sliding bar with the right until the opening 

 is a little wider than necessary. Place cover-glasses on base-plate, bring 

 sliding bar into apposition with covers, and the holder is prepared for 

 taking a spread. A small projecting pin at end of plate secures covers 



* Brit. Med. Journ., 1904, ii. p. 1635. f Tom. cit., pp. 759-60 (1 fig.). 



