Question: What were sausage casings made from originally?
About the article "Sausage", section "Casings".

Candidate passages:
Traditionally, sausage casings were made of the cleaned intestines, or stomachs in the case of haggis and other traditional puddings.
Today, however, natural casings are often replaced by collagen, cellulose, or even plastic casings, especially in the case of industrially manufactured sausages.
Some forms of sausage, such as sliced sausage, are prepared without a casing.
Additionally, luncheon meat and sausage meat are now available without casings in tin cans and jars.
Artificial casings are made of collagen, cellulose, or even plastic and may not be edible.
Artificial casings from animal collagen can be edible, depending on the origin of the raw material. 
Natural sausage casings (“casings”) are made from the sub-mucosa, a layer of the intestine that consists mainly of naturally occurring collagen.
This should not be confused with collagen casings, which are artificially processed from collagen derived from the skins of cattle.
Natural casings are derived from the intestinal tract of farmed animals, are edible and bear a close resemblance to the original intestine after processing.
The outer fat and the inner mucosa lining are removed during processing.
Natural casings are traditional products that have been used in the production of meat specialties for centuries and have remained virtually unchanged in function, appearance, and composition.
Salt and water are all that is used for cleaning and preservation.
Natural casings are the only casings that can be used in organic sausage production.
A large variety of sausage is produced world-wide using intestines of pigs, sheep, goats, cattle and sometimes horses.
Although the intestines were previously flushed, scraped and cleaned by hand, more recently, machinery has been used for large scale production. 
Teewurst is a German sausage made from two parts of raw pork (and sometimes beef) and one part bacon, which are minced, seasoned and packed in casings (mostly porous artificial casings) before being smoked over beech wood.
The sausage then has to mature for seven to ten days in order to develop its typical taste.
Teewurst contains 30 to 40 percent fat, which makes it particularly easy to spread.
Teewurst was invented in Pomerania, probably in the small Baltic town of Rügenwalde (now Darłowo in Poland), in the middle of the 19th century.
The name, which means "tea sausage", is said to derive from the habit of serving sandwiches at teatime.
Up to 1945, the sausage industry in Rügenwalde was well established, and Teewurst was its best-known product.
In 1927, the term "Rügenwalder Teewurst" was declared a Protected designation of origin.
After World War II, sausage makers from Rügenwalde fled or were expelled to the Federal Republic of Germany, where they established new companies and resumed the production of Teewurst.
They established an association of former Rügenwald sausage makers, which registered the trademark "Rügenwalder Teewurst" in 1957.
Today, only companies that once had their headquarters in Rügenwalde are allowed to use the term "Rügenwalder Teewurst".
All others use the terms "Teewurst" or "Rügenwalde-style Teewurst". 
Plastic casings are extruded like most other plastic products.
They also can be flat or shirred.
Generally, smoke and water do not pass through the casing, so plastic is used for non-smoked products where high yields are expected.
The inner surface can be laminated or co-extruded with a polymer with an affinity for meat protein causing the meat to stick to the film, resulting in some loss when the casing is peeled, but higher overall yield due to better moisture control.
Plastic casings are not commonly used any more due to health hazards.
Plastic casings are generally made from polymers such as Polyamide, Polypropylene or Polyethylene.
Polyamide (Nylon) plastic casings are the most commonly used in production of cooked sausages and hams such as luncheon meat and bologna.
Polyamide casings come in two main varieties: Oriented and non-oriented.
The oriented polyamide are shrinkable casings and will shrink during the cooking process thereby reducing the water loss.
Non-oriented polyamide casings remain the same diameter during the cooking process and thereby allow for expansion of the meat during cooking.
The use of polyamide casings has expanded recently with the advent of various varieties and structures of casings such as multilayer casings USPTO Patent No.
4,243,074 (Hoechst AG) [http://www.archpatent.com/patents/4243074.