From: ara@zurich.ai.mit.edu (Allan Adler)
Newsgroups: sci.bio
Subject: cutting a leaf
Date: 25 Jul 92 15:41:05 GMT
Article-I.D.: camelot.ARA.92Jul25104105
Distribution: sci
Organization: M.I.T. Artificial Intelligence Lab.



I found a book in the library that I really like: Microscopy of Vegetable 
Foods, by Andrew L. Winton and Josef Moeller, NY John Wiley&Sons, 1906.

I am sure I will return to this newsgroup with many questions as I read
the book, but right now I am hung up just getting started. This is partly
due to the fact that although the authors recommend that one have a good
background in microscopy, I don't feel I do, and also to the fact that I
am working at home instead of in a well equipped laboratory.

On p.28, there is a nice picture of a leaf in cross section, Fig.11, followed
by a more detailed examination of the various parts. On p.30, there is a
short paragraph on "Preparation of Materials", presumably for preparing such
a cross section for examination. It begins: "Sections are cut with a razor,
holding the leaf between pieces of pith."

Alas I have no pith. I wouldn't know where to look for it. A more modern book
on histological technique assumes one will normally be using a microtome and
explains how to  embed (human) tissues in paraffin and mount them
in the microtome. So I gather that the point is that I want something firm
enough to hold the object (leaf) I wish to cut and which is at the same time 
soft enough that I can cut both it and the leaf, like a sandwich.

I am not sure what I should use to hold the leaf while I do this. And I am
also concerned that if it firm enough to hold it, it might also squeeze and
damage the leaf when I sandwich the leaf in it.

The book on histological technique (Histological Technique for Normal and
Pathological Tissues and the Identification of Parasites, by H.M.Carleton
and R.A.B Drury, 3rd ed., Oxford U.Press, 1957) is rather terse but 
contains a lot of useful information. For example, apart from discussing
different methods of preparing specimens for the microtome, it also gives 
a table of errors in section cutting and their remedies (p.66), such
as that the section comes out curved or curls up or any number of things
that could be wrong. And it says how to strop and hone the knife blade, etc,
and advises one to examine it under the microscope to make sure that even
at the microscopic level it is smooth enough and has the right shape,
lest it tear or damage the specimen.

I assume the same applies mutatis mutandis to the little razor blade I would
use on the leaf.

So it seems that even though all I want to do is make a little section of
this leaf and look at it, there is already a lot for me to worry about.

I should also mention the microscope I am using. I picked up a nice one in
India about 11 years ago for about $100 (which was 2/3 of month's salary).
It can magnify from about 50x to about 675x. I have no oil immersion lens.
It has an iris and condenser and a micrometer stage, a mirror but no
light source (and I lack a suitable light source), no polarizing filters,
etc. I look at things sometimes and usually find so much chromatic aberration
from the different parts of the specimen that I can't make much out. 
Hopefully, by examining things like onion skin instead of dandruff, this
situation will improve. In the past, I have managed to see my own sperm,
and on another occasion I discovered that a little "splinter" in my hair
was a louse using this scope. Others have told me I got a pretty good deal on 
this microscope, so I think the problems I consistently have with it are due to
my lack of technique and to problems that are really inherent in what I am 
trying to study. I have no stains or other materials for fixing or mounting
specimens, other than slides and cover, and no tools other than a razor blade,
a pair of tweezers and an alcohol lamp.

Allan Adler
ara@altdorf.ai.mit.edu