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Through a Lens. Brightly.
- University Press of New England
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153 p p p p p p p p p p p p p p p p p throughalens.brightly. The microscope has been extolled as the most important invention in the history of biology, and I don’t dispute this. Of the fourteen weekly laboratory exercises I schedule for my introductory biology course, the use of the microscope is the one I always look forward to with the greatest sense of anticipation, because there is usually one student who is so captivated by the experience that his or her curious mind becomes a hungry one, as if, like a specimen on a slide, it has also been illuminated. The microscope was invented in the Netherlands in the sixteenth century, and it boggles me to consider that it was not turned to biological materials in any significant way until a hundred years later. It was left to the brilliant, restless, melancholic Englishman Robert Hooke to publish a collection of observations called the Micrographia—the first serious work of biological microscopy, and biology has never been the same since. It’s easy to follow in Hooke’s footsteps in the undergraduate laboratory because cells of all kinds are exceedingly easy to gather. An onion will yield a limitless supply of plant cells that, properly prepared for observation, resemble a brick wall. A drop of water from a drainage ditch sets the mind spinning with countless single-celled organisms that glide and swarm without cease. One small, delicate, translucent leaf of the freshwater plant Elodea shows cells packed with tiny green bodies called chloroplasts—the seats of photosynthesis—that circulate in the cytoplasmic current, faster and faster as one increases the light. In fact, when I was a high schooler I was told that they stream counterclockwise in the northern hemisphere and clockwise in the southern. Although I have long since been disabused of this notion, I have never been able to shake the hankering to take a trip Down Under to see for myself. 154 p b o u n d l e s s m o m e n t s But what about animal cells? As my students stand gathered about my desk, I explain that they will harvest these from their own bodies. Then I allow the silence to fester and swell as they wonder how and precisely from where they will glean these cells. The most easily accessible place is the lining of the mouth. The moist membranes of the inside of the cheeks are constantly shedding thin, flakelike epidermal cells. It’s a way of renewing that delicate stratum after we assault it with caustic things like Pepsi, vinegar, hot foods, and jalapeña peppers—the sooner the body gets rid of these damaged cells, the better. We swallow— or spit out—countless numbers of them every day. It would be a shame not to take advantage of the windfall in the biology laboratory . The process is painless. A couple of gentle scrapes with the flat side of a toothpick does it. Then it’s just a matter of stirring the cells in a drop of water on a slide, adding a bit of iodine stain to render them visible, and mounting the slide on the stage of the microscope. I have never had a student who wasn’t able to make an exemplary preparation of cheek cells. And it’s the rare student who isn’t pleased, or even elated, by the sight. They look like soggy cornflakes. But their salient feature is the perfect nucleus that occupies the center of these cells. On one occasion I leaned over a student’s shoulder and whispered, “Just think. That nucleus has all of your genes. We could take that nucleus and make a copy of you. A clone. Just think.” (I’ve often wondered if that student hesitated to rinse off the slide after he had completed his observations.) I was given a microscope when I was seven, and promptly used it to look at my spit. Considering my early exposure to the instrument, it is always slightly jarring to see how many of my college-age students have never used a microscope. Rather than the child’s élan, they tend to bring apprehension to their first interaction with the scope, regarding it as being as complicated as the flight panel of an aircraft. My students’ inexperience has led to some interesting mo- [54.242.75.224] Project MUSE (2024-03-19 06:06 GMT) Through...