What is catgut actually made from?

Stefan Pociask:

What connects cats, tennis, doctors, cows, and violins? The surprising answer is... catgut!

Catgut sutures have been used for a long time. Indeed, catgut is still the material used for creating absorbable stitches. These are stitches that dissolve on their own and don’t need to be removed. Producing catgut remains a profitable industry, given the ongoing demand. But where does it actually come from?

If your cat is by your side as you read this, don’t worry—Fluffy doesn’t need to be concerned. Catgut has never been made from real cat intestines. While it is theoretically possible to use a cat's intestines for making catgut string, it doesn't compare to the much longer strings you get from cows and sheep. A cow's intestine can yield up to 160 feet of catgut string, which is far more substantial than what you’d get from a cat’s smaller intestines. So why is it called catgut if no cats are involved? I’ll explain shortly. But first, let’s explore exactly what catgut is.

These days, catgut is primarily derived from the intestines of cows, although occasionally it can be from sheep, pigs, or even horses. However, cow-sourced catgut remains the largest industry. When cows are processed for meat, their intestines are saved and then processed. Here’s a cross-section of an intestine:

The portion of the intestine used to create catgut is mostly taken from the submucosa and externa layers, both of which contain collagen—the protein that gives the string its necessary strength and flexibility. Collagen is found throughout the bodies of mammals and other vertebrates in areas where soft tissues need structural support and elasticity. Take skin, for example, which must be both durable and stretchy. The intestines also require similar strength and stretch—when we consume food, the intestines need to expand without tearing and then return to their normal size afterward. The collagen in these tissues consists of strong, stretchable fibers.

In slaughterhouses, intestines are typically sliced lengthwise into halves, thirds, or quarters. This produces varying thicknesses, depending on the intended use. The above cross-section is divided into two, three, or four long strips. These strips are then soaked in several solutions and caustic solvents, which dissolve away the tissue, leaving only the tough collagen fibers. Once purified, these fibers are stretched, twisted, and dried under tension. The result is catgut string, which is one of the strongest strings available by weight. In fact, it’s stronger than an equal weight of steel wire.

Catgut is manufactured in various diameters, based on its intended application. It finds its place in three key industries. The first is in medicine, where it serves as a surgical suture material. While it has been largely supplanted by other absorbable materials in western countries, it remains in high demand in developing regions.

The second primary use of catgut is in sports, especially in tennis and other racket sports. For these applications, catgut—originally used for racket strings—is made thicker to meet the durability requirements.

As a biological material, catgut does degrade over time. However, it provides the perfect blend of strength and flexibility. This makes it ideal for archery bows, a use that dates back to ancient Egypt. While the Egyptians were fond of cats, they didn’t use them for bows. Even back then, catgut was sourced from cattle.

The third major application of catgut is in stringed instruments. It was once the standard material for violin strings. Though there are now many alternatives, catgut still has a place in professional orchestras, found on a range of instruments—from classical guitars to the large pedal harps that produce ethereal sounds.

Now that you know no cats were harmed in the making of catgut, you might be curious why it’s called catgut. The gut part is clear—it refers to the material’s origin in intestines, an old word. However, the cat part originally came from the word kytte (pronounced “kit”). So, what is a kytte? Here’s what it looks like:

This is the front and back of a kytte, a tiny violin from the medieval period. It was so small that it could be tucked into a pokett, which comes from the Old French poque, meaning bag. Traveling minstrels would pull out their kyttes, play a lively tune, and then safely stow the sturdy instrument back in the pokett without worrying about the fragility of a full-sized violin. These instruments were an ideal pairing of a horsehair bow and a cow-gut string, perfectly complementing each other. In essence, catgut (kytte gut) is named for the gut used to string your kytte. It has nothing to do with cats at all.

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