CUTTING SECTIONS 



499 



on a plate of glass which has been wetted with glycerin and gently 

 warmed. The melted paraffin is now poured into this mould and 

 the object is imbedded in it as described for the paper tray. 



Still another plan is to take a common flat medicine-bottle, as in 

 fig. 409, fitted with a cork through which two tubes pass, or, if the 

 mouth is small, one tube may be fastened into a hole drilled into the 

 bottle. One of these tubes, A, is connected with hot and cold water ; 

 the other, JB, is a discharge -pipe for the water entering the bottle 

 by A, and raising or lowering its temperature as warm or cold water 

 is allowed to flow in. On the smooth, flat side of the bottle four 

 pieces of glass rods or strips are cemented fast, so as to inclose 

 a rectangular space, C, which for*ms a receptacle 

 for the melted paraffin. 



As long as the warm water circulates through 

 the bottle the paraffin remains fluid, and objects 

 in it may be arranged under the microscope by 

 light from above or below, and can be oriented 

 with reference to the sides of the paraffin recep- 

 tacle or with reference to lines drawn upon the 

 surface of the bottle. When the cold water is 

 allowed to enter in place of the warm, the paraffin 

 congeals rapidly, and may be easily removed as 

 one piece. The discharge-pipe should open near 

 the upper surface of the bottle, to draw r off any 

 air which may accumulate there. 



In using any form of microtome where the 

 object is held in jaws, the imbedding mass must 

 either be cast a suitable shape, and placed directly 

 in the jaws, or be cemented to pieces of soft 

 wood which may be placed in the jaws. 



The mould obtained by either of these pro- 

 cesses is then fixed to the carrier of the micro- 

 tome, and finally pared into a convenient shape, 

 and oriented for cutting. 



4. Cutting. Paraffin sections are always cut 

 dry that is, the knife is not \vetted with either 

 alcohol or any other liquid. 



; If the knife be set square that is, with its 

 axis at right angles to the line of motion (of the 

 knife for sliding microtomes, and of the object- 

 carrier for rocking microtomes) and if the paraffin block be 

 cut into a rectangle, and also set square that is, with one edge 

 parallel to the edge of the knife sections may be cut in " ribbons." 

 The sections not being removed from the knife one by one as they 

 are cut, but allowed to lie undisturbed on the blade, adhere to one 

 another by the edges so as to form a chain or ribbon, which may be 

 taken up and transferred to a slide without breaking up, thus greatly 

 lightening the labour of mounting a series.' 



Difficult objects are in general better cut in isolated sections 

 with an oblique knife. In this case it is best to cut the paraffin into 

 the shape of a three-sided prism, and arrange it so that the knife- 



K K 2 



FIG. 409. Arrange- 

 ment for the orien- 

 tation of objects in 

 paraffin. 



