Grinding 



GROUND SECTIONS 



81 



oml)e(l(ling in balsam is described in some 

 detail iu the .second example wiiich follows 

 the chapter and need not be repeated here. 



Selection of Grinding and Polishing 

 Agents 



Once the initial sections have been pre- 

 pared it is necessary that they should have 

 one face pohshed, that this polished face 

 should then be attached to some mate- 

 rial, and that tlie other face be j^round 

 away and brought to a pohsh when the 

 section is of the correct tliickness. One 

 technique for doing this is described in 

 the first example at the end of this chap- 

 ter, but some discussion must take place 

 at this point as to the selection of grinding 

 and pohshing agents. 



The initial flattening of one side of the 

 section is best done with the aid of carbo- 

 rundum powder, using a grit of about 100- 

 mesh. The 100-mesh carborundum itself is 

 far too coarse to leave a surface wliich may 

 be polished and an intermediate stage is 

 required. In the writer's opinion, pumice 

 is best used for this intermediate stage. 

 We are now speaking of relatively soft 

 material, such as bone or coral, and not of 

 thin slices of rock which would require 

 several stages of carborundum between 

 100-grit and pumice. One of the most diffi- 

 cult things to determine is when the 

 scratches have finally been removed; this 

 can never be seen when the sections are 

 wet from grinding. It is, therefore, neces- 

 sary at intervals to wash the surface of the 

 section which is being ground, to dip it 

 into alcohol, and then to warm it until dry. 

 The surface of the section is then ex- 

 amined with a strong hand lens by re- 

 flected light, and grinding is ceased when 

 it presents a uniform, dull surface un- 

 broken by scratches. 



The next stage is to bring this flattened 

 surface to a high degree of polish. All the 

 old directions recommend the use of rouge . 

 The objection to rouge is its color, and the 

 fact that it gets over everything on the 

 bench and around the bench. The author 

 most warmly recommends the substitu- 

 tion of white rouge (eerie oxide), which is 

 rapidly replacing ordinary rouge in the 

 polisliing of glass, and is also excellent for 

 microscopical specimens. It does not mat- 

 ter very much against what surface the 

 abrasive has up to this time been rubbed, 

 though glass is conventional. It is, how- 

 ever, impossible to get a fine surface with 

 rouge on glass and one should, therefore, 

 use a leather strop for the purpose. This 

 does not mean a loose leather strop of the 

 type used by barbers but rather a flat 

 surface of horsehide which has been at- 

 tached to a hardwood block. Rubbing the 

 section up and down on this, while it is 

 well lubricated with a slurry of white 

 rouge, will soon bring it to a fine pohsh. 

 There is no reason to get discouraged if, 

 after polishing, the surface is found still to 

 have a few fine scratches on it. The sec- 

 tions are going to be mounted in balsam 

 which will hide most of the scratches. 



The sections are then cemented, pol- 

 ished side down, to a shde and ground on 

 some flat surface with coarse carborundum 

 until they are of the required thickness. It 

 is unfortunate that there is no adequate 

 method of judging this thickness except by 

 eye; experience is the only guide which 

 may be reasoriably followed. As soon as 

 the section has been ground down to the 

 required thickness it is then smoothed 

 with pumice, polished with white rouge, 

 and finally mounted. Practical appUcation 

 of the principles here discussed will now 

 be given in the form of two typical 

 preparations. 



Typical Examples 



Preparation of a Section of Bone 



If the worker is interested only in the 

 production of a section which will show 

 the existence of Haversian canals, it is 

 better to decalcify the bone (in one of the 

 solutions given under AF 20 in Chapter 

 19) and to prepare sections by the paraffin 



technique described in Chapter 12. These 

 sections, however, show neither the lamel- 

 lae, lacunae, or canalicuh, which can only 

 be demonstrated in a section prepared by 

 grinding, in which all the calcareous parts 

 remain intact. 



