60 MATERIALS AND PROCESSES OF SLIDE-MAKING 



The first thing to do is to wet the underside of the bottom of the paper box 

 in the water and press it firmly into contact with the plate-glass slab which 

 will both hold it in position and assist in cooling the wax. Then take (Fig. 

 28) one of the beakers of molten embedding material from the oven and fill 

 the little paper box to the brim. Heat the pipette in the flame to a tempera- 

 ture well above that at which the wax will melt. Use it to pick up the object 

 from its own dish (Fig. 29) and to transfer it to the little paper boat. By the 

 time that this has been done, a layer of hardened wax will have been formed 

 at the bottom of the paper boat, so that the object will rest on the layer of 

 solidified wax with a molten layer above it. It will happen almost invariably 

 that the surface has also cooled, so that a crust of cool wax will have been 

 carried down with the object into the box. It is essential to get rid of this if 

 the wax is to adhere through section cutting. Reheat the pipette; use it to 

 melt the entire surface of the box (Fig. 30) and to maneuver the object into 

 the approximate position in which it is required to lie in the finished block. 

 Then blow on the surface until the wax is sufficiently solidified to enable you 

 to pick up the box carefully and, as shown in Fig. 31, hold it on the surface 

 of the water used for cooling. With most wax media it is desirable to cool the 

 block as rapidly as possible, and it should never be permitted to cool in air. 

 It cannot, however, be pushed under the surface of the water because the mol- 

 ten center is liable to break through the surface crust and thus destroy the 

 block. After holding the box in the position indicated until it is fairly firm 

 throughout, push it under the surface to complete the cooling. 



The block may be left in water for any reasonable length of time, but if it 

 is to be stored for days or weeks it is much better kept in a 5 per cent solution 

 of glycerin in 70 per cent alcohol. There seems to be a widespread delusion that, 

 because an object must be perfectly dehydrated before being impregnated with 

 wax, it must subsequently be kept out of contact with fluids. Nothing could 

 be farther from the truth. As will be discussed later, when dealing with the 

 actual technique of sectioning, it is often desirable to expose a portion of the 

 object to be sectioned and leave it under the surface of water for some days in 

 order to get rid of the brittleness which has been imparted through the embed- 

 ding process. Blocks which have been stored dry for a long period of time should 

 always be soaked in a glycerin-alcohol mixture for at least a day before sectioning. 



It is, in any case, undesirable to section a block as soon as it has been made, 

 because it is necessary for successful sectioning that the block be the same 

 temperature throughout. If a block is made in the evening, it is better to take 

 it out of the water and to leave it lying on the bench overnight, in order that 

 the temperature may be stabilized. 



