Mounting block 



PARAFFIN SECTIONS 



113 



much better for him to secure a series of 

 small rectangular blocks of some hard 

 wood like maple and to soak these for a 

 day or two in molten wax. After they are 

 removed, drained, and cooled it is the sim- 

 plest thing in the world to atta(;li a paraf- 

 fin block to them and to hold them in the 

 jaws of the microtome. Whether the metal 

 holder or the wooden one are used, the 

 technique is essentially the same. A layer 



bring these buttresses so far up the block 

 that thoy reach the tip of the ol)ject to be 

 cut. The metal should now be placed on 

 one side and allowed to reach room tem- 

 peratui-o. Many people at this point throw 

 the block and holder into a fingerbowl of 

 water, which is all right provided the wa- 

 ter is at room temperature. But there is 

 no more fruitful source of trouble in cut- 

 ting sections than to have the knife, the 



Fig. 64. Mounting the wax block on the block holder. 



of molten wax is built up on the surface 

 and allowed to cool. The block (see Fig. 

 64) is then pressed lightl}' onto this hard- 

 ened wax and fused with it with the aid 

 of a piece of heated metal. Some people 

 use old scalpels but the writer prefers the 

 homemade brass tool shown in the figure. 

 Care must be taken to press only very 

 lightly with the forefinger and to perform 

 the whole operation as speedil}^ as possible 

 to avoid softening the wax in which the 

 object is embedded. The metal tool should 

 be heated to a relatively high temperature 

 and touched hghtly to -the base of the 

 block. If the block is very long, it is also 

 desirable to build up small buttresses of 

 wax against each side, being careful not to 



block, and the microtome at different 

 temperatures. It is much better to mount 

 the blocks the day before one intends to 

 cut them and to leave them on the bench 

 to await treatment. A final inspection is 

 then made of the block to make certain 

 that its upper and lower surfaces are flat, 

 smooth, and parallel. Many people do not 

 make the final cuts on these surfaces until 

 after the block has been mounted in the 

 block holder. The block and the block 

 holder, after insertion in the jaws of the 

 microtome, are seen in Fig. 65 and it will 

 be noticed that setscrews on the apparatus 

 permit universal motion to be imparted to 

 the block so that it can be correctly orien- 

 tated in relation to the knife. It is easy to 



