| Abstract: | The thickness of ultrathin tissue sections embedded in Epon-Araldite and cut with a diamond knife was measured by re-sectioning and electron microscopic examination of the section profiles. A secondary section mounted on a Formvar-coated slot grid provided enough normally cut segments (seven to seventeen) for measurements giving a precise estimate of mean thickness, comparable to that obtainable by interference microscopy (±2.3% or less for grey to dark gold sections). The standard deviation of section thickness within sections was never more than 5 nm, corresponding to a coefficient of variation of 6.5% or less for sections more than 48 nm thick. This suggests that variation in section thickness, within sections, may be less than has been supposed, so that quantitative work may be based on thickness measurements made over a limited representative area. A silver interference colour was associated with sections 49–60 nm thick. |
