1 66 PARAFFIN SECTIONING. {CHAP. VII 



the block of paraffin in the holder of the microtome so that the tissue will be at 

 the proper level for cutting. If a ribbon microtome is used, heat the holder and 

 melt the end of the block upon it. Cool and place the holder in its place in the 

 microtome. Use a very sharp, dry razor for cutting the sections. The sections 

 are made with a rapid, straight cut as in planing. Do not try to section with a 

 drawing cut as in collodion sectioning. If the temperature of the room is right 

 for the paraffin used, the sections will remain flat, and if the opposite sides of the 

 block are parallel, and one edge strikes the knife squarely, the sections will 

 adhere and thus make a ribbon. If the room is too cold for the paraffin the sec- 

 tions will roll. If it is too warm the sections will be imperfect. 



Remember the sections must be very thin, from 3/u to 15^ to show fine structural 

 details to good advantage. 



I 274. Extending- the Sections with Warm "Water. — Paraffin sections are 

 liable to be very finely wrinkled. These wrinkles in the sections often obscure the 

 structure. To remove them, the ribbons or separate sections are placed on cold 

 water in a dish like a waste jar ( Fig. 135). Then hot water is slowly added till 

 the sections extend. This removes the folds. When the water has cooled, the 

 ribbons are cut into proper lengths with scissors, and the pieces transferred to 

 albumenized slides. 



\ 274a. Extending Sections on the Slide. — Instead of placing the sections 

 on water in a dish, the sections may be put directly upon slides. To extend them, 

 add sufficient water so that they will float. Warm the slide carefully until they 

 straighten, pour off the water, and allow the slides to stand for several hours 

 until all the water has evaporated. The sections adhere firmly to the slide and 

 are in optical contact with it, as shown by the shiny appearance when all the water 

 has evaporated. 



\ 275. Fastening the Sections to the Slide. — To fasten the sections firmly to 

 the slide, coat the slide with albumen fixative (# 297) as follows : Put a minute 

 drop of the albumen on the center of a slide and with a clean finger spread the 

 albumen over the slide, wiping off all that is possible. Finally beat or tap the slide 

 with the end of the finger. This will make a very thin ( it cannot be too thin ) and 

 even layer. Place the sections in position and allow them to remain until the 

 water has all evaporated. It is well to leave them over night. After the water 

 has evaporated, coat the sections with ?4'ths% collodion, using a delicate brush for 

 the purpose. Allow the collodion to dry for a minute or two, then put the slides 

 in benzin or xylene to dissolve the paraffin (see § 276). If the sections are not 

 extended on water, they may be put directly on the albumenized slides, pressed 

 down with the finger and coated with collodion. This is much more rapid, but 

 does not get rid of the fine folds. See also the preface for albumenizing slides. 



# 276. Removing the Paraffin. — Immerse the slide in a vessel of xylene or 

 benzin. This will dissolve the paraffin. An hour will usually suffice. One can 

 hasten the solution of the paraffin by moving the slide in the solvent. In this way 

 it may be dissolved in 5 to 10 minntes, or even less. It will do no harm to leave 

 the slide in the benzin or xylene over night. Two or three days even might not 

 do any harm, but it is usually better to proceed at once to the other operations. 



\ 277. Removing the Xylene or Benzin — From the xylene or benzin plunge 

 the slide bearing the sections into a jar of 95^ alcohol, and leave it for a few 

 minutes, or move it around in the alcohol for half a minute or so. 



\ 278. Staining the Sections with an Alcoholic Dye. — With an alcoholic 



