MAKING SECTIONS 65 



inserted into the microtome. Since the majority of sections today are cut on a 

 Spencer rotary microtome, the following description is of the use of one of the 

 holders supplied with this machine, although the ingenuity of man has not 

 yet succeeded in devising a worse method of attaching a paraffin block to a 

 microtome. The holder, which is seen in Fig. 37, consists of a disc of metal with 

 a roughened surface attached to a cylindrical shank. First of all, this disc must 

 be covered with a layer of wax, and it is extraordinarily difficult to get wax to 

 adhere to these chromium-plated surfaces. If the worker is not entirely bound 

 by convention, it would be much better for him to secure a series of small 

 rectangular blocks of some hardwood like maple and to soak these for a day 

 or two. in molten wax. After they are removed, drained, and cooled, it is the 

 simplest thing in the world to attach a paraffin block to them and to hold 

 them in the jaws of the microtome. Whether the metal holder or the wooden 

 one is used, the technique is essentially the same. A layer of molten wax is 

 built up on the surface and allowed to cool. The block (see Fig. 37) is pressed 

 lightly onto this hardened wax and fused to it with the aid of a piece of heated 

 metal. Some people use old scalpels, but the author prefers the homemade 

 brass tool shown in Fig. 37. Care must be taken to press very lightly with 

 the forefinger and to conduct the whole operation as speedily 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 applied by just touching 

 it lightly. If the block is very long, it is also desirable to build up small but- 

 tresses of wax against each side, being careful not to bring these buttresses so 

 far up the block that they reach the tip of the object to be cut. The metal 

 should now be put aside and allowed to reach room temperature. Many people 

 at this point throw the block and holder into a finger bowl of water, which 

 is all right provided the water is at room temperature. However, there is no 

 more fruitful source of trouble in cutting sections than to have the knife, the 

 block, and the microtome at different temperatures. It is much better to mount 

 the blocks the day before they are to be cut and to leave them on the bench to 

 await treatment. Then final inspection is made of the block to make certain 

 that the upper and lower surfaces of the block 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. 38. It will be noticed 

 that set screws on the apparatus permit universal motion to be imparted to 

 the block, so that it can be orientated correctly in relation to the knife. It is 

 easy to discover whether or not the edges are parallel by lowering the block 

 until it does not quite touch the edge of the knife, adjusting it until the lower 



