84 



THE ART OF MAKING MICROSCOPE SLIDES 



Bone 



unless the specimens are reground with 

 pumice. The final polish can be judged by 

 eye and should be such as would be 

 acceptable on, say, a pohshed ivory 

 ornament. 



The slide is then returned to the hot 

 table seen in Fig. 31 and heated until the 

 balsam is molten. Another slide is placed 

 alongside the first, liberally smeared with 

 balsam, and the sections transferred from 

 the first shde to the second with the pol- 

 ished side down. They must be pressed 

 hard to make sure that the polished side 



necessary that the shde should not rock 

 from side to side as it is pushed about, or 

 the covershps will become ground at the 

 end before the sections of bone in the mid- 

 dle are thin enough. Experienced experts 

 can often grind a section of bone until it is 

 as thin as a number 1 coverslip, but this is 

 not recommended to the beginner, for if 

 the section is ground too thin it will sud- 

 denly disintegrate and all the work done 

 so far will be lost. When the sections are 

 judged to be thin enough, the slide is very 

 carefully washed under the tap to remove 



Fig. 32, Grinding down bone slabs. 



is in contact with the glass. The shde is 

 then cooled and returned to the glass plate 

 (Fig. 32) containing the carborundum 

 paste, on which it is now slowly and stead- 

 ily ground until the sections are thin 

 enough. The thickness may partly be esti- 

 mated by holding the specimen up to a 

 Ught and seeing how transparent it is be- 

 coming; the correct thickness has the 

 transparency of a rather thin sheet of oiled 

 paper. If the technician does not care to 

 trust his judgment in the matter it is pos- 

 sible to take two number 3 coverslips and 

 to cement one on each end of the slide. 

 A thick number 3 covershp is about the 

 thickness of a good section of bone so that, 

 if the bone is ground down until the cover- 

 shp just starts to be affected by the grind- 

 ing compound, the sections may be pre- 

 sumed to be of the right thickness. To use 

 this method satisfactorily, however, it is 



all traces of carborundum grit and the sec- 

 tions then smoothed with pumice, as was 

 done before. A certain amount of reduc- 

 tion in thickness may also be produced by 

 the pumice though it is usually better to 

 use carborundum. As soon as the scratch 

 marks of the carborundum have been re- 

 moved, the sections are again washed care- 

 fully under the tap and then pohshed. A 

 coverslip is then placed on top of the prep- 

 aration and the slide examined under vari- 

 ous powers of the microscope, which will 

 verj^ soon disclose whether or not it is thin 

 enough. If it is not thin enough to show 

 the required structures it should be taken 

 back to the carborundum, ground some 

 more, then resmoothed and repohshed in 

 the manner described above. Several trials 

 are often required before all the sections 

 are found to be satisfactory. 



There are two schools of thought as to 



