Histotechnology I- Miscellaneous
Question No. 20. The Answer is: (D) Caused by vibration of the block, the block holder, or the knife.
Discussion: The ripple-like light and dark bands observe a rather strict periodicity and are perpendicular to cutting action of the ultramicrotome. This type of artifact is typically caused by a high frequency vibration of the cutting system that involves either the block, the block holder, or the knife. The vibration introduces a forward and backward type of movement of the block against the knife during sectioning. How to tell from this photo? There is a knife mark here (delineated by the white arrows). Knife marks are always perpendicular to the direction of movement of the block on sectioning.
Knife marks are never this periodical nor this wide as illustrated here. Insufficient osmium or inappropriate curing will not lead to this type of artifact. Inhomogeneous staining will lead to rather distinct patches of under stained or unstained areas with a blur margin. On the other hand, there is a faint staining water mark due to suboptimal staining as illustrated by the red arrow. Please note the curvy shape of this water mark which reflects the rolling shape of the section because of the vibration artifact (red arrow). Also note that the section above this curvy line is slightly more darkly stained then the section below this line.