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April 3, 2018

Miniature Staircases

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Long story short, from Atlas Obscura:

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Miniature staircases made between

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the eighteenth and twentieth centuries

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by members of a secret society of French woodworkers

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known as compagnons.

April 3, 2018 at 12:01 PM | Permalink | Comments (1)

BehindTheMedspeak: "The lens of the eye is the only transparent tissue in the human body"

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Above, the first sentence of Ralf Dahm's Scientific American article "Dying to See." More:

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In the past few years, scientists have determined that this transparency — critical for focusing light — stems in large part from the unique ability of the lens to activate a self-destruct program in its cells that aborts just before completion, leaving empty but sustainable cells that transmit visible rays.

A better understanding of how lens cells become and remain transparent should suggest ways to prevent lens-clouding cataracts.

Beyond protecting vision, improved knowledge of how the lens tightly controls cell suicide could reveal ways to treat debilitating conditions characterized by inappropriate or excessive cell death, chief among them Parkinson's disease, Alzheimer's disease, and chronic infections such as AIDS.

The eye's lens is a biological marvel, being at once dense, flexible and clear.

Transparency in nature is unusual because cells have organelles - internal structures such as the nucleus, mitochondria, and the Golgi apparatus and endoplasmic reticulum, which are important in the synthesis of proteins and lipids.

Each structure has its own refractive index, and when a light ray crosses an area where the index changes, the light scatters, creating a degree of opaqueness.

Furthermore, many cells, including those in hair and skin, are populated with melanins - pigment molecules that come in colors ranging from red to black.

The lens has no melanin and no blood supply.

Yet that alone is not enough for transparency.

Cartilage has no melanin or blood supply and is colorless, but it is at best translucent.

That is because in virtually all tissues, cells or fibers are oriented at various angles, creating different refractive indices that scatter light as it passes through.

The lens is composed of only one cell type, and the cells are precisely aligned.

Is the lens even alive, being that it has no blood supply, no connective or nervous tissue, and no organelles?

If life means a cell has a metabolism, then lens cells are alive — albeit barely.

Young lens cells do have organelles when they first form from stem cells in a fetus, but the organelles are destroyed during early development.

Although they have no mitochondria to produce energy, certain nutrients and other molecules diffuse into the lens's outermost cells and slowly pass inward, cell to cell.

The lens is a "biological crystal" — that is, it has a very regular arrangement of cells.

Each cell contains large molecules — crystallin proteins — that form complexes with paracrystalline arrangements.

This construction makes the cytoplasm optically homogenous; the refractive index does not change inside the cell or from one cell to another.

Although lens cells survive the controlled suicide of organelles, this degradation has drastic implications.

Without nuclei, the genetic programs for synthesizing new parts are gone.

Mature lens cells cannot regenerate or repair themselves, as cells in other tissues do.

Within six months or so, 90% of the cells that make up our bodies are replaced by new ones.

Lens cells must function for a lifetime — a spectacular span.

This lack of repair mechanism makes the cells vulnerable to certain stresses.

For example, severe dehydration can cause crystallin proteins to precipitate, prompting their cells to crumble into a clump — a cataract.

This speck disrupts the otherwise uniform index of refraction, creating a cloudy spot in a person's field of vision.

Just a few weeks of extreme dehydration can initiate cataract formation.

The ability of lens cells to begin the process of cellular suicide and then halt it just short of total destruction has come as a surprise to scientists, who have up to now always considered such self-destruction — termed "apoptosis" — to be an unstoppable process.

Some unknown mechanism in the lens controls the death machinery so it destroys only certain cell components while leaving others intact.

Once this became apparent, the next leap in thinking came quickly: a mechanism that could control apoptosis could alter the progression of diseases characterized by excessive cellular suicide, such as neurodegenerative disorders.

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Before reading the article, I hadn't known that dehydration could cause cataracts.

I don't recall hearing a peep about it during my ophthalmology rotation during my third year of med school.

On the other hand, that was 1972-73, and maybe such a relationship hadn't been established way back then.

Anyhoo.

Elderly people are frequently hospitalized due to dehydration.

Could it be that cataracts could be prevented by encouraging constant ongoing fluid intake in seniors, even when they're not thirsty?

Perhaps cataracts are not an inevitable accompaniment of aging alone, but rather the result of the decreased fluid intake that seems to accompany aging.

The human lens is amazingly similar in structure to an onion.

I wonder if studying the biology of onions — how they happen to develop their layered structure — could be helpful in understanding how it is that the human lens attains its unique shape and underlying framework.

More on the lens here.

April 3, 2018 at 10:01 AM | Permalink | Comments (0)

bookofjoe's Favorite Thing: Libman Extra Wide Angle Broom

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The crew who painted my house last summer left one of these brooms behind, under the bushes in front.

I only discovered it last fall when I was outside against the front of my house with a ladder cleaning the gutters.

I was struck by how heavy the broom was compared to the generic corn iteration I've always used around the house.

Then I gave it a floor test and I understood what a good broom should do: though my found broom is old, it sweeps clean.

Highly recommended.

You can too!

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$29.97.

April 3, 2018 at 08:01 AM | Permalink | Comments (0)

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