Faults observed during section-cutting PDF

Preview

Summary

Download Faults observed during section-cutting PDF

Description

PROBLEM

Sections fail to form ribbons

REASON Surfaces and edges of the block are not parallel Horizontal surface of the block is not parallel to the knife Paraffin wax is too hard Knife is tilted too much Sections are too thick

Sections roll up on cutting so that they adhere and get broken against the knife edge

Ribbon is curved, crooked or uneven instead of straight

A hole is formed in the section

Re-adjust and reorient the block Coat horizontal edges of the block with wax of lower melting point Reduce the tilt

Knife is dull Knife is blunt Tilt of knife is too great Knife edge is dirty

Clean the knife edge

Blunt or dull spot on the knife, producing an irregular knife edge

Adjust the knife so that knife edge will present a uniformly sharp edge to the block, or sharpen

Edges of the block are not parallel but round or wedge shaped

Re-trim the block

Knife is not parallel to the block

Readjust the knife and block

Knife edge is coated with paraffin Sections are too thin Microtome set screw is loose Tilt of knife is too vertical

Sections are squashed (width of each section is less than that of the block)

Re-trim the block

Readjust the thickness of the sections Hone and strop Sharpen the knife Reduce the tilt

Knife is blunt or dull Paraffin block is warm and soft Sections are compressed, wrinkled or jammed

REMEDY

Bevel of knife is lost due to incorrect sharpening Bubble or dirt formed in the embedding medium Tissue is not processed properly and will not form a section (especially if center is raw) Under-processed portion of tissue bursts on contact with warm water Hard spot in tissue

Re-sharpen the knife Cool the block on ice water until firm Clean the knife edge Readjust thickness of the section Tighten the screw Reduce the tilt Re-sharpen, using a knife back or automatic knife sharpener Re-embed in freshly filtered wax if necessary

Re-process tissue

Re-process tissue

Once embedded in

due to calcium

paraffin wax, decalcification is

impractical; use a base-sledge microtome with a wedge knife

Sections of unequal thickness are produced

Tilt of knife is too great or bevel is not cleared, hence object is compressed against the knife edge Clamp set screw on knife or block holder is loose Blocks are too large Blocks are too hard

Sections adhere to the knife or other parts of the microtome

Ribbon is split or lengthwise vertical scratches are seen on sections

Sections are lifted from the knife on upstrokes

Resistance is felt on the lower part of the section during cutting

Horizontal or parallel lines or furrows across the section ("chatters") are seen

Static electricity due to low atmospheric humidity

Knife edge is dirty Knife edge is dull Knife tilt is too great Nicks or damage on the knife edge Dirty embedding Knife edge is dirty Tilt of knife is too great Knife tilt is too great Knife is dull Paraffin is too soft or room temperature is warm Tilt of knife is too small, paraffin block is therefore compressed against the base of the knife towards the end of stroke Knife edge vibrates due to hardness of tissue Tilt of knife is too great Knife is blunt Knife is not clamped properly

Section cut is sometimes thin, sometimes thick

Knife or block holder is loose Knife tilt is too small that block is compressed by bevel and section is not cut

Reduce the tilt

Tighten the screw Cut blocks into smaller fragments Soften the blocks in detergent or phenol Breathe out or blow gently on the block and knife to break up static electricity, or boil water in the room to increase humidity Clean the knife edge Sharpen the knife Reduce the tilt Sharpen the knife Re-embed in freshly filtered wax Clean knife edge with xylene Reduce the tilt Reduce the tilt Sharpen the knife Cool paraffin wax in ice water

Increase the tilt

Treat with phenol during processing or collodionize Reduce the tilt Sharpen the knife Adjust the knife so that knife edge will present a uniformly sharp edge to the block, or sharpen Tighten adjusting and locking screws

Increase the tilt...