HOW TO TEASE A TISSUE. 27 



background, e.<j., black paper; if coloured, a white one. In the 

 latter case, however, the shadows interfere with exact vision, and it 

 is better to support the slide upon an object raised slightly above 

 the white background. This is readily accomplished by placing it 

 over a white porcelain capsule, or on a photophore (fig. 28), into 

 which is slipped a piece of white paper. 



In a laboratory, one of the most convenient ways is to have the 

 tables painted of a black or very dark green colour, but the painting 

 must be flat, with no shining varnish. At the edge of the table is 

 painted a white strip i J inches broad. Some prefer to burn into 

 the surface of the table solid paraffin blackened by means of lamp- 

 black. Others use porcelain slabs one-half black and the other 

 white. 



Photophore (fig. 28). This is a small wooden box, 5 cm. high, 

 9 cm. long, and 9 cm. broad. The upper part is formed of glass. 

 The front wall of the box is Avanting. 

 Placed obliquely within the box is a 

 mirror, which reflects the light upwards 

 through the glass cover and the slide to 

 the eye of the observer. 



In dissociating with needles, we must FlG 28 ._pi 10 toi-,ii<>re. 



have some knowledge of the arrange- 

 ment of the parts of the object to be teased, such as the direction 

 of the fibres, itc. Take a small piece only. Always tease one end 

 of the tissue, and fix the latter with one needle while the parts are 

 separated with the other needle. 



One of the most convenient combinations is that of Kterhod, 

 which combines a photophore with a turntable. The wheel of the 

 latter can be removed, and the block forms not only a photophore, 

 but also a surface on which tissues of different colours can be teased 

 and mounted. 



VI. FIXING AND HARDENING REAGENTS. 



Most of the tissues and organs must be hardened in suitable 

 fluids before they can be cut into sections. A large number of 

 fluids of various kinds are used, each organ or tissue requiring its 

 own appropriate fluid. Some organs, <?.*/., bone, are too hard to be 

 cut in their natural condition ; they must be decalcified by appro- 

 priate fluids. Amongst others, the following fluids are required, 

 but others are referred to in the text. 



A. Alcohol. 



Alcohol is one of the most important hardening fluids used 



