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A syringe nowadays nearly always means a medical syringe, but it can mean any of these:
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 undesirable, as it may cause an air embolism; preventing embolisms by removing air from the syringe is the reason for the familiar image of holding a hypodermic syringe upside down, tapping it, and expelling a small amount of liquid before an injection into the bloodstream.
The barrel of a syringe is made of plastic or glass, and usually has graduated marks indicating the volume of fluid in the syringe. Glass syringes may be sterilized in an autoclave, however, modern medical syringes are made from plastic because it is cost-effective to dispose of them, which further reduces the risk of spreading blood-borne diseases. The re-use of needles and syringes has been associated with the spread of diseases, especially HIV and Hepatitis among IV drug users.
Disposable medical syringes are sometimes used without a needle for orally administering liquid medicines to young children or 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.
Syringes for insulin users are designed for standard U-100 insulin. The dilution of insulin is such that 1ml of insulin fluid has 100 standard "units" of insulin. Since insulin vials are typically 10ml, each vial has 1000 units.
Insulin syringes are made specifically for self injections and have friendly features:
There are needle syringes designed to reload from a built-in tank (container) after each injection, so they can make several or many injections on a filling. These are not used much in human medicine because of the risk of cross-infection via the needle. An exception is the personal insulin autoinjector used by diabetic patients.
In certain 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.
Medical-grade disposable hypodermic syringes are often used in chemistry laboratories for its convenience and low cost. They are often used for measuring and transferring solvents and reagents where a high precision is not required.
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.
Used with a long needle or cannula, syringes are also useful for transferring fluids through rubber septa when atmospheric oxygen or moisture are being excluded. Examples include the transfer of air-sensitive or pyrophoric reagents such as phenylmagnesium bromide and n-butyllithium respectively. Glass syringes are also used to inject small samples for gas chromatography (1 μl) and mass spectrometry (10 μl). Syringe drivers may be used with the syringe as well.
Some culinary uses of syringes are injecting liquids (such as gravy) into other foods, or for the manufacture of candies, such as Fruit Gushers.
Syringes may also be used when cooking meat to enhance flavor and texture by injecting juices inside the meat, and in baking to inject filling inside a pastry.
Syringes are used to refill ink cartridges with ink.
Sometimes a large hypodermic syringe is used without a needle for very small baby mammals to suckle from in artificial rearing.
To administer enemas or douches, there are bulb syringes where a bulb is fitted with a nozzle, liquid is pumped into it, the nozzle is inserted into the rectum or vagina and the bulb is pressed upon for injection.
There are fountain syringes where the liquid is in a bag or can and goes to the nozzle via a pipe. In earlier times, clyster syringes were used for that purpose.