question: How do syringes work? Why does liquid only come out when it is pressed on?
comment: The liquid is held in by surface tension. In the same way that tiny water drops can stay a drop and not just spread out into a very thin sheet, the end of the needle is small enough that surface tension keeps the liquid from flowing out. Pushing on the plunger provides a force strong enough to break that sirface tension, and the liquid comes out.
passages: Loose snus is often applied using modified syringes. The nozzle is removed so the opening is the width of the chamber. The snus can be packed tightly into the chamber and plunged into the upper lip. Syringes, called portioners, are also manufactured for this particular purpose.
  
  Syringes that are able to administer medication can be used to act as cap guns, where the projectile is not usually a cap but can be paper or aluminium pellets.
  
  Section::::Historical timeline.
   Medical syringes are sometimes used without a needle for orally administering liquid medicines to young children or animals, or milk to small young animals, because the dose can be measured accurately and it is easier to squirt the medicine into the subject's mouth instead of coaxing the subject to drink out of a measuring spoon.
  
  Section::::Medical syringes.:Tip designs.
  
  Syringes come with a number of designs for the area in which the blade locks to the syringe body. Perhaps the most well known of these is the Luer lock, which simply twists the two together.
   An oral syringe is a measuring instrument used to accurately measure doses of liquid medicine which are expressed in millilitres (mL). They do not have threaded tips, because no needle or other device needs to be screwed onto them. The contents are simply squirted or sucked from the syringe directly into the mouth of the person or animal.
  
  Oral syringes are available in various sizes, from 1–10 mL and larger. The sizes most commonly used are 1 mL, 2.5 mL and 5 mL.
  
  Section::::Medical syringes.:Dental syringes.
   Once the drugs are dissolved, a small syringe (usually 0.5 or 1 cc) is used to draw the solution through a filter, usually cotton from a cigarette filter or cotton swab (cotton bud). "Tuberculin" syringes and types of syringes used to inject insulin are commonly used. Commonly used syringes usually have a built-in 28 gauge (or thereabouts) needle typically 1/2 or 5/8 inches long.
   A 3-way syringe/nozzle has separate internal channels supplying air, water or a mist created by combining the pressurized air with the waterflow. The syringe tip can be separated from the main body and replaced when necessary.
  
  In the UK and Ireland, manually operated hand syringes are used to inject lidocaine into patients' gums.
  
  Section::::Medical syringes.:Governmental control of syringes.
  
  In some jurisdictions, the sale or possession of hypodermic syringes may be controlled or prohibited without a prescription, due to its potential use with illegal intravenous drugs.
  
  Section::::Non-medical uses.
  
  The syringe has many non-medical applications.
  
  Section::::Non-medical uses.:Laboratory applications.
   Currently, the design of the low dead space needle incorporates a plastic neck that fits within the neck of a standard syringe hub.
  
  Section::::Detachable Needle Design.:Low dead space syringe.
  
  This design is accomplished by using a standard syringe body with an extended plunger that inserts into the neck of the syringe body to expel more fluid from the syringe.
  
  Section::::WHO Guidelines for people who inject drugs.
   The first hypodermic needle was first used by Dr. Alexander Wood and immediately efforts were made to improve the design. It was not until 1954, with the need for massive syringe distribution of Dr. Salk's polio vaccine, that the first disposable syringes were created. Initially made of glass, in 1961 plastic disposable syringes became available. The advent of the first low dead space syringe occurred with the creation of 1-ml syringes designed specifically for the administration of insulin. Then amongst the scare of HIV and rising concern of other communicable diseases to healthcare workers the creation of safety syringes occurred in 1988. As of the last few years new designs have emerged that work on a needle that is low dead space and fits onto and transforms high dead space syringes into low dead space syringes. One design achieves this by creating a plunger that inserts itself into the syringe neck to expel as much fluid as possible from the syringe body, thus reducing the amount of space available within the neck.
   BULLET::::- 1899: Letitia Mumford Geer of New York was granted a patent for "In a hand-syringe the combination of a cylinder, a piston and an operating-rod which is bent upon itself to form a smooth and rigid arm terminating in a handle, which, in its extreme positions, is located within reach of the fingers of the hand which holds the cylinder, thus permitting one hand to hold and operate the syringe..."
   The barrel of a syringe is made of plastic or glass, usually has graduated marks indicating the volume of fluid in the syringe, and is nearly always transparent. Glass syringes may be sterilized in an autoclave. However, most modern medical syringes are plastic with a rubber piston, because this type seals much better between the piston and the barrel and because they are cheap enough to dispose of after being used only once, reducing the risk of spreading blood-borne diseases. Reuse of needles and syringes has caused spread of diseases, especially HIV and hepatitis, among intravenous drug users. Syringes are also commonly reused by diabetics, as they can go through several in a day with multiple daily insulin injections, which becomes an affordability issue for many. Even though the syringe and needle are only used by a single person, this practice is still unsafe as it can introduce bacteria from the skin into the bloodstream and cause serious and sometimes lethal infections. In medical settings, single-use needles and syringes effectively reduce the risk of cross-contamination.
   The word "syringe" is derived from the Greek σύριγξ ("syrinx", meaning "Pan flute", "tube").
  
  Section::::Medical syringes.
   Particularly for intravenous administration, self-injection in the arm can be awkward, and some people modify a syringe for single-handed operation by removing the plunger and affixing a bulb such as from a large dropper or baby pacifier to the end of the barrel to in effect make it a large dropper with a needle affixed. This is therefore a variant of the common method of injection with a dropper with the hypodermic needle affixed, using a "collar" made of paper or other material to create a seal between the needle and dropper. Removing part of the plunger assembly by cutting off most of the shaft and thumb rest and affixing the bulb to the end of the barrel, thereby allowing the bulb to operate the plunger by suction, also does work in many cases.
   Greiner Bio-One manufactured the first ever plastic evacuated blood collection tube in 1985 under the VACUETTE brand name. Today, many companies sell vacuum tubes as the patent for this device is now in the public domain. These tubes are manufactured with a specific volume of gas removed from the sealed tube. When a needle from a hub or transfer device is inserted into the stopper, the tube's vacuum automatically pulls in the required volume of blood.
   Sectors in the syringe and needle market include disposable and safety syringes, injection pens, needleless injectors, insulin pumps, and specialty needles. Hypodermic syringes are used with hypodermic needles to inject liquid or gases into body tissues, or to remove from the body. Injecting of air into a blood vessel is hazardous, as it may cause an air embolism; preventing embolisms by removing air from the syringe is one of the reasons for the familiar image of holding a hypodermic syringe pointing upward, tapping it, and expelling a small amount of liquid before an injection into the bloodstream.
   Bodies featuring a small, plain connection are known as slip tips and are useful for when the syringe is being connected to something not featuring a screw lock mechanism.
  
  Similar to this is the catheter tip, which is essentially a slip tip but longer and tapered, making it good for pushing into things where there the plastic taper can form a tight seal. These can also be used for rinsing out wounds or large abscesses in veterinary use.
   The two ends of the cannula are inserted through the septa covering donating and receiving flasks. The cannula extends below the surface of the fluid to be transferred. A vacuum is applied to the receiving flask, and the low pressure relative to the donating flask causes the fluid to flow through the cannula.
   Fittings and adapters used to fill evacuated tubes from butterfly needle kits and syringes are also available.
   Low dead space syringe
  
  A Low dead space syringe is a type of syringe with a design that seeks to limit dead space that exists between the syringe hub and needle.
  
  Section::::Differences between low and high dead space syringes.
   Syringe filter
  
  A syringe filter (sometimes called a wheel filter if it has a wheel-like shape) is a single-use filter cartridge. It is attached to the end of a syringe for use. Syringe filters may have Luer lock fittings, though not universally so. The use of a needle is optional; where desired it may be fitted to the end of the syringe filter.
   Pills such as prescription opiates or benzodiazepines which are often converted by users into crude injectables, have ingredients such as chalk and wax as a filler, and illicit drugs are often adulterated with cutting agents to increase profits. Correctly used, wheel filters with at least pore size 0.5 µm may reduce these impurities entering the blood stream and help avoid vein problems such as collapsed veins, abscesses, infections, embolism, 'dirty tastes', disease and sepsis.
   There is also an eccentric tip, where the nozzle at the end of the syringe is not in the centre of the syringe but at the side. This causes the blade attached to the syringe to lie almost in line with the walls of the syringe itself and they are used when the blade needs to get very close to parallel with the skin (when injecting into a surface vein or artery for example).
  
  Section::::Medical syringes.:Standard U-100 insulin syringes.
   Septa (singular: septum) are rubber stoppers which seal flasks or bottles. They give an airtight seal, preventing the ingress of the atmosphere, but are able to be pierced by sharp needles or cannulae.
  
  Section::::Equipment.:Cannula.
   The two ends of the cannula are connected similarly. The receiving flask is connected to its own gas bubbler, while the donating flask is connected to a source of inert gas. By increasing the inert gas pressure, the pressure within the donating flask is raised higher than the receiving flask, and the fluid is forced through the cannula.
   Safety syringes have a safety mechanism built into the syringe. The needle on a safety syringe can be detachable or permanently attached. On some models, a sheath is placed over the needle or the needle retracts into the barrel following injection to protect healthcare workers and others from accidental needlestick injuries. Another option is a secondary device, such as Oak Ridge Products needle capper that allows the user, with one hand, to apply a cover over the contaminated needle. The importance of the safety syringe has increased; legislation requiring it or equivalents has been introduced in many nations since needlestick injuries and re-use prevention became the focus of governments and safety bodies.
   BULLET::::- An "air-in-line" detector. A typical detector will use an ultrasonic transmitter and receiver to detect when air is being pumped. Some pumps actually measure the volume, and may even have configurable volumes, from 0.1 to 2 ml of air. None of these amounts can cause harm, but sometimes the air can interfere with the infusion of a low-dose medicine.
  
  BULLET::::- An "up pressure" sensor can detect when the bag or syringe is empty, or even if the bag or syringe is being squeezed.
   The polyethylene construction of these disposable syringes usually makes them rather chemically resistant. There is, however, a risk of the contents of the syringes leaching plasticizers from the syringe material. Non-disposable glass syringes may be preferred where this is a problem. Glass syringes may also be preferred where a very high degree of precision is important (i.e. quantitative chemical analysis), because their engineering tolerances are lower and the plungers move more smoothly. In these applications, the transfer of pathogens is usually not an issue.
  
raw_presuppositions: Syringes should be leaking liquid since the tip is open.
raw_corrections: The liquid in a syringe is held in by surface tension.