DIATOM TEST SLIDE BY R.I. FIRTH

Dated 1962

R.I. Firth 8 form Test slide. This slide actually contains 10 diatoms, being bordered by Arachnoidiscus ehrenbergii on each side. The first six were resolved to the level of the puncta at 40X with S-Plan objectives. The striae of Nitzschia were resolved at 40X with oblique illumination, but required 100X oil immersion to resolve the puncta. The striae of Synedra capitata could be resolved at 40X but the puncta were resolved only with a high n.a. oiled darkground condenser, and the 100X Apo objective with built-in iris. I could not resolve the puncta of this diatom with 100X DIC oil immersion with the same objective.