SECTION CUTTING. 51 



brass cylinder or well. This box is provided with an exit-tube 

 (H), to allow the water resulting from the melting of the ice to 

 escape. The size of the cylinder varies from 1-2 inches in 

 diameter, but for most purposes one with a diameter of i inch will 

 be found sufficient. The ice-box is covered on the outside with a 

 thick layer of gutta-percha. Professor Hamilton, of Aberdeen, first 

 suggested the addition of a glass top to be screwed upon the plate 

 of the instrument. 



By far the most convenient cutting tool for use with this micro- 

 tome is an ordinary planing-iron fitted with a handle, as recommended 

 by Delepine (fig. 35). 



Above all, the tissue must have been properly hardened, and 

 previously steeped in a freezing fluid, either gum mucilage or gum 

 and syrup, after removal of all alcohol from it (p. 50). 



In using this instrument, screw the plug down to the necessary 

 depth, thus making a well of the required depth at least half the 

 depth of the cylinder and into the well drop a few drops of 

 glycerine, or put a little lard round the line of contact of the plug 

 and the cylinder. This is to prevent any of the fluid passing down 

 between the plug and the cylinder. 



Fill the ice-box with a mixture of pounded ice and salt, and 

 pack it well around the central brass cylinder. Keep a cork in 

 the exit tube H, and only allow the fluid to flow away when it 

 accumulates in large amount. In a short time the temperature of 

 the plug is greatly reduced. Pour into the well a little mucilage 

 (BP), sufficient to form a layer about J- inch thick, and allow this 

 to freeze. The piece of tissue taken from the freezing mixture is 

 lifted with a pair of forceps, and put into the well, so that it 

 touches and adheres to that part of the well farthest away from the 

 operator. 



AVhen the tissue is fixed, fill up the well with mucilage and 

 cover it with a piece of sheet india-rubber, and keep the latter 

 in position by a weight. This is to prevent the entrance of the 

 freezing mixture into the well. 



Supposing the tissue to be frozen, the operator seizes the 

 elevating scre\v P with his left hand, and in his right holds the 

 planing iron, which is fixed in a wooden handle. With the left 

 hand the operator turns the screw, i.e., elevates the tissue, while as 

 rapidly as he chooses with his right hand the planing iron, firmly 

 pressed on the glass plate at (about) an angle of 45, is pushed 

 rapidly forwards and drawn backwards, and in a few seconds 

 twenty or thirty sections accumulate on the upper surface of the 

 planing iron. By means of a large camcl's-hair brush they are 

 transferred to a large quantity of water, whereby the gum contained 

 within them is dissolved and the sections themselves uncurl. One 



