Hello all,

Here in Sydney, a group of us have been getting agitated about spherical
aberration:  To the extent that we see it as the major preventable
limitation on confocal performance (particularly "penetration")

In the course of our discussions, we have discovered that we have only very
fragmentary information about the refractive index of living material.

Of course, there is a lot of biological tissue out there and it is definite
that  not all of it has the same RI. Even individual cells are mixtures
(Why else would be see phase contrast?).

We have found a few isolated estimates of about 1.45 (a LONG way from both
1.515 (oil) or 1.33 (water)) but feel that there may be more and better
estimates out there for specific tissues. What we are looking for is a sort
of average value: what you would get from say 100 micrometers of randomly
overlapped cells or a certain type: maybe with (or without?) extracellular
material such as cellulose and collagen. There may be figures for muscle,
or cornea or lens.

If you have either made specific measurements yourself or know of published
figures, I would very much appreciate hearing what they are.

Cheers,

Jim P.
              ****************************************
Prof. James B. Pawley,    (on Sabbatical)       Ph.  61-2-9351-7548/2351
Room LG 10, Madsen Building, F-09,              FAX  61-2-9351-7682
University of Sydney, NSW, 2006 Australia       [log in to unmask]
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"A scientist is not one who can answer questions but one who can question
answers."       Theodore Schick Jr., Skeptical Enquirer, 21-2:39