1. Demonstration of the optical disector
Zheng-Wei Yang
Morphometric Research Laboratory
North Sichuan Medical College
Nanchong city, Sichuan province, China
(This English version is written on 2 July 2010 as suggested by Nigel G. Wreford & Robert I. McLachlan, Australia)

2. Introduction to the animated cartoon on page 4: The cartoon consists of 15 consecutive optical sections (spaced 1 m apart) observed through a high aperture oil immersion lens within a single 25 m thick methacrylate-embedded (physical) section of rabbit testis. Particles seen in the sections are nuclei of spermatids approximating spheres. Superimposed on the sections are 4 counting frames (each 21  15 m), around which the profiles (sections) of 16 nuclei (a-p) formed on the optical sections Nos are indicated.

3. Question: If we count nuclei from the 3rd optical section down to the 13th optical section, i.e. count the nuclei within the 10 m (thickness) of section between the 3rd and 13th sections, which nuclei should be counted “within” the 4 counting frames (disectors)?
Answer: Starting at the 3rd optical section all nuclei are counted as they come into focus “within” the counting frame according to the disector counting rule[1-2]. That is, we count newly appearing nuclei. See page 5 for further answers.
References
Sterio DC. The unbiased estimation of number and sizes of arbitrary particles using the disector. J Microsc 1984; 134(Pt 2):
Gundersen HJ et al. The new stereological tools: disector, fractionator, nucleator and point sampled intercepts and their use in pathological research and diagnosis. APMIS 1988; 96(10):

4. Play this slide to see an animated cartoon showing the optical disector

5. Upper left frame: All 3 nuclei (a, b, c) should be counted.
Upper right frame: 4 nuclei (d, e, f, g ) should be counted; 1 nucleus (h) should not.
Lower left frame: 2 nuclei (i, j ) should be counted; 1 nucleus (k) should not.
Lower right frame: 4 nuclei (m, n, o, p) should be counted; 1 nucleus (l ) should not.