130 



THE ART OF MAKING MICROSCOPE SLIDES 



T. S. intestine 



paper, and placed in one of the stender 

 dishes which has been filled to the brim 

 with the molten embedding medium. 

 Under no circumstances should a hd be 

 placed on the stender dish since it is desir- 

 able that as much as possible of the benzol 

 should evaporate while the process of em- 

 bedding is going on. After about an hour 

 the specimen should be removed to fresh 

 wax in the second stender dish, where it 

 may remain another hour, and then to the 

 third stender dish where it should not re- 

 main for more than thirty minutes. 



Shortly before the end of this last hour a 

 decision should be made as to what type 

 of vessel is to be used for casting the 

 block, and it would be difficult to improve 

 on a paper box (Fig. 50) for this object. 

 The box having been made (it should be of 

 ample size) it is moistened at the bottom 

 and placed on a slab of glass in the manner 

 described earlier in this chapter. The box 

 should be about half filled with embedding 

 material from the beaker and allowed to 

 remain until the layer of wax has con- 

 gealed on the bottom. An object like the 

 one under discussion is best handled with 

 an old pair of forceps rather than with a 

 pipet. The forceps should be warmed in a 

 flame to well above the melting point of 

 the wax, and moved backward and for- 

 ward across the surface so as to melt the 

 surface film which has formed. The object 

 is then rapidly picked up from its stender 

 dish, placed in the wax, and enough fresh 

 wax from the beaker added to make sure 

 that there will be as much solid wax above 

 as there is underneath the specimen. 

 Blocks of this nature shrink greatly, and 

 it will probably be best to fill the box en- 

 tirely full. As soon as the box has been 

 filled, the forceps should again be warmed 

 and passed backward and forward around 

 the object to make sure that no film of un- 

 molten wax (which would cause it conse- 

 quently to cut badly) remains. The wax in 

 its box should now be blown on until it 

 starts to congeal on the surface, then very 

 carefully picked up with the fingers and 

 lowered into a dish of water at room tem- 

 perature until the water does not quite 

 reach the top of the box. If it be thrust 

 under the surface at this point, all of the 

 molten wax will come out and the block 



be rendered useless. As soon, however, as 

 the block is seen to be congealed through- 

 out, it is thrust under the surface of the 

 water and something laid on it to keep it 

 at the bottom. It should be left in the 

 water for at least five or six hours and 

 much better overnight. 



One now sets up the microtome, and 

 makes sure that the knife is sharpened in 

 the manner previously described, and then 

 mounts the block. The block having been 

 trimmed to size and mounted as noted 

 earlier, there remains only the actual cut- 

 ting. The block should be trimmed so 

 there is at least as much wax on each side 

 of the object as there is in object itself. 

 This amount of wax would be excessive 

 were we preparing serial sections, but for 

 the preparation of individual sections of 

 this type, in an example given for the 

 benefit of the beginner, this quantity is 

 desirable. The handle of the microtome 

 should now be rapidly rotated and the be- 

 ginnings of the sections observed. There is 

 no need to worry if the section curls to one 

 side or the other during this preliminary 

 period, since the entire area of the block 

 will not be cut until twenty or thirty sec- 

 tions have been removed. As soon, how- 

 ever, as the knife is seen to be approaching 

 the object, and the block in its entirety is 

 being cut, the ribbon must be observed 

 most carefully to see that it is suffering 

 from none of those defects indicated in the 

 table of defects. Should the ribbon not be 

 coming perfectly, various suggestions 

 given in the table may be tried until a 

 perfect ribbon is secured. Since we are not, 

 in this case, preparing a series of sections, 

 it is unnecessary to cut a longer ribbon 

 than will contain the actual number of 

 sections required, with a few left over for 

 emergencies. It is, however, a great mis- 

 take to throw i)artially cut blocks away, 

 since they may be stored in a glycerol- 

 alcohol mixture ciuite indefinitely, and one 

 never knows when further sections may 

 be required. The block, however, should 

 be labeled before being placed in its solu- 

 tion by writing the appropriate informa- 

 tion on a piece of paper and fusing this 

 with a hot needle into an unwanted por- 

 tion of the block. 



Each section is now cut individually 



