Reagents and Processes. 383 



Cutting and Mounting Paraffin Sections. —For cutting paraffin 

 sections some form of microtome must be used.' The smaller 

 student forms may be made to perform very efficient service in paraffin 

 sectioning. 



After the material has been imbedded, as described under Imbedding 

 in Paraffin, page 386, cut out a small block of paraffin containing the 

 object to be sectioned ; melt a small piece of paraffin on the end of a pine 

 block I centimeter square in cross section and about 2 centimeters long, 

 and while the paraffin on the end of this stick is still melted, press into 

 it and firmly against the stick the paraffin block containing the object. 

 The paraffin block should be so placed on the stick that when the latter 

 is fastened upright in the object carrier of the microtome, the microtome 

 knife v,i\\ cut the sections in the desired direction through the object. 

 Heat a wire nail or dissecting needle, and melt the base of the paraffin 

 block superficially, to seal it more firmly to the stick. Submerge the 

 stick in cold water to harden the paraffin, and fasten it in the object 

 carrier of the microtome, having first set the carrier near its lowest 

 position. Adjust the stick so that the top of the paraffin block just 

 touches the under surface of the knife. Set the knife at right angles to 

 the bed of the microtome. Trim the face of the paraffin block which 

 faces the knife parallel with the edge of the knife, and to about i milli- 

 meter from the object, and trim the opposite edge of the block in the 

 same manner, so that the two edges are parallel, and parallel to the 

 knife edge. Then trim the remaining two sides of the block rather 

 close to the object. The sections should now adhere in a ribbon as they 

 are cut ; 10 micromillimeters is a good average thickness for the sections 

 (i micromillimeter = j-j^y^ millimeter). In wielding the knife see that 

 the knife carrier runs easily in its bed (using oil if necessary), rest the 

 elbow upon the table, and make short strokes with a wrist motion 

 simply. Transfer the ribbons of sections to a clean tray, keeping the 

 side down which was down in cutting, and finally mount the sections on 

 the glass slip in the same position. 



To mount the sections on a glass slip, spread a few drops of albumen 

 water over that portion of the slip which is to be occupied by the 

 sections, the slip having first been washed with soap and water, rinsed, 

 and polished by rubbing it vigorously with a clean cloth. If the albumen 

 water has a tendency to creep away from the place where it has been 



1 For description of microtomes see catalogue of Bausch & Lomb, Roch- 

 ester, N.Y. 



