Stefan Pociask:

What do cats, tennis, doctors, cows, and violins have in common? The answer is … catgut!

Catgut sutures have been around a long time. Yes, catgut is what is used to make absorbable stitches, even today. Absorbable stitches are those that don’t need to be removed; they just kind of break down and become part of your skin. Making catgut is a pretty lucrative business, as there is still a fair demand for the material. But where does it come from?

If your cat is sitting with you as you read this, you can tell Fluffy not to worry: catgut is not—and never has been—made from actual cat guts. Theoretically, you could use a cat’s intestines to make catgut string, but when compared to the string you get from cows and sheep, it’s not worth the trouble. A cow intestine can produce catgut string that is up to 160 feet long. Your cat’s intestine is small potatoes, compared to that. So why the hell is it called catgut when no cats were harmed in the production of this string? I’ll
get to that in a bit. First, let’s find out exactly what this string is.

These days, catgut comes mostly from the intestines of cows—though sometimes it's sheep, pigs, or even horses. But cow catgut is the biggest current industry. When cows are slaughtered for meat, the intestines are saved and processed. Here is a cross section of intestine:

Quora

The part that is used to make catgut comes mostly from the submucosa and the externa layers, both of which contain collagen, which is the protein we're looking for. Collagen is found throughout the bodies of mammals and some other vertebrates. Wherever structural strength and elasticity is required in soft tissue, you may find collagen there. Skin, for instance, which is strong and elastic. The intestines also need to be strong and elastic; when we eat a lot of food, for instance, we needthe intestines to stretch without bursting—and then to contract back to normal size after the food passes. This collagen is made up of strong stretchy fibers.

At slaughterhouses, the intestines are usually slit in half, thirds, or quarters, lengthwise. This would make different thicknesses, for different uses. So the above cross-section would make two, three, or four long lengths. These are then soaked in a series of solutions and caustic solvents, which dissolve away all the tissue except for the strong collagen fibers. Once all these fibers are clean and pure, it is then stretched, twisted, and allowed to dry under tension. What remains is catgut string which, pound for pound, is one of the strongest strings there is. In that regard, it’s stronger than a comparable weight of steel wire, in fact.

Various gauges (or diameters) of catgut are produced, depending on what its ultimate use will be. There are three main industries where catgut is used: The first is as surgical suture material. In western countries, it is being replaced by other materials that also are absorbed into the body, but the market is still strong in developing countries.

The second industry is sports, namely tennis and other racket sports. For sporting purposes, catgut—which was the original racket material—is made much thicker.

Since catgut biological material, it does degrade with time. But it offers the perfect combination of strength and "spring." As such, catgut has long been used to string bows for archery, at least as far back as ancient Egyptian times. And as we know, the Egyptians really loved their cats. So clearly they didn’t use their intestines for their bows. No, even then, catgut was made from cattle.

The third major use of catgut is for for stringed instruments. Catgut was the original violin string material. These days, there are many other types of strings, but you can still find catgut in many professional orchestras, on a variety of instruments, from classical guitars to those giant pedal harps that rest against your shoulder and make Heaven-like sounds.

Now that you know that no kitties were harmed in the making of catgut, you may be wondering why it was ever called catgut. Well, the gut part is obvious: it’s made out of guts, which itself is a very old word. But the cat part actually started out as kytte (pronounced “kit”). What is a kytte? This is a kytte:

Quora

That’s the front and back of a kytte—a medieval-era mini-violin. It was so mini, that it was stored in the pokett, which was derived from the Old French poque, or bag. Traveling minstrels could whip out their kyttes, play a lively tune or three, and then put their hardy instrument back into their pokett without worrying about the delicate frailty of a normal-sized violin. These instruments were the perfect mingling of a horsehair bow, rubbing against a cow gut catgut, in perfect concert with each other. Basically, catgut (kytte gut) is so named because it is gut that is used to string your kytte. Simple as that. It has nothing to do with felines whatsoever.

This post originally appeared on Quora. Click here to view.