EXERCISES IN THE PREPARATION OF TISSUES. 



Blocks for cutting are now made by forming cells with a couple of 

 L-shaped strips of lead resting on a glass plate. Into these paraffin is 

 poured to the top, and the piece of tissue is submerged, with warmed 

 forceps or needles, into the position required for cutting. When the 



Mould of L-shaped strips of metal for embedding in paraffin. 



surface of the paraffin has solidified plunge the whole cell into cold 

 water to complete the solidification, then strip the block of its cell and 

 it is ready to attach to a microtome. 



Small pieces of fresh tissue of this thickness () may be dehydrated, 

 penetrated with clove oil, and saturated with paraffin by 20 minutes' 

 exposure to each reagent, assisted by slight warmth. If ten times the 

 volume of the tissue be used, and the fluids are individually changed three 

 successive times, a block can be made ready for cutting in about an 

 hour. 



Horse-shoe microtome. Clamp the razor blade in position with 

 its shoulder clear of the frame. Raise the regulating screw until 

 the back of the frame is close to the glass ; the razor edge is now 

 fully elevated above the glass plate, from this the height of the 

 paraffin block is gauged. Pare the latter to the required thickness, and 

 attach it to the glass plate. The glass must be free of moisture ; 

 melt the block to it with a hot wire or blade of an old scalpel, and 

 bank some paraffin around its foot to give a broad base of attachment. 

 Trim the front and back faces of the block straight and parallel to each 

 other. Secure the glass plate to the table with a piece of moist 

 blotting paper. The left hand holds the carrier, the thumb and 

 forefinger of the right hand grasp the regulating screw, the other 

 fingers lying 011 the frame as an additional guide, the wrists rest upon 

 the table and by a simultaneous movement of both hands the frame is 

 carried forward with a quick and even swing to which the weight of 



