injection, introduction of a fluid into the body, usually by means of a needle and syringe. The material injected may be a test substance (as in determining allergic sensitivity or immunity to a disease), an anesthetic, a therapeutic drug, a nutrient (in cases where intravenous feeding is necessary), blood, or blood plasma (see blood transfusion). An intracutaneous injection is the introduction of a small amount of fluid between the skin layers. A subcutaneous injection is directed to the tissues under the skin. When quicker absorption of a drug is required, an intramuscular injection may be used; even more rapid action is obtained by injection into a vein (intravenous). In certain emergencies involving the heart, such as cardiac arrest, an intracardiac injection can penetrate directly into a chamber of the musculature of the heart. Anesthetics are sometimes injected into the spine. In an injection by means of a jet injector gun, fluid penetrates through the skin by means of air pressure and there is no visible puncture mark. Micro-injections can be made into fetuses, even individual cells, with tiny capillary injectors.

In an internal-combustion engine, introduction of fuel into the cylinders by a pump rather than by the suction created by the movement of the pistons (see piston and cylinder). On diesel engines, which lack spark plugs, the heat created by compressing air in the cylinders ignites the fuel, which has been pumped in as a spray. In engines with spark ignition, fuel-injection pumps are often used instead of conventional carburetors. Fuel injection distributes the fuel more evenly to the cylinders than does a carburetor; more power can be developed and undesirable emissions are reduced. In engines with continuous combustion, such as gas turbines and liquid-fueled rockets, which have no pistons to create suction, fuel-injection systems are necessary.

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Injection may refer to:

  • Injection (medicine), a method of putting liquid into the body with a syringe and a hollow needle that punctures the skin.
  • Injective function in mathematics, a function which associates distinct arguments to distinct values
  • Injection molding, a manufacturing technique for making parts from thermoplastic and thermosetting material
  • Injection (economics), a financial boost entered into the economic cycle, includes government spending, investment and exports
  • Injected (band), an American rock band from Atlanta, Georgia formed in 1995
  • Code injection, a technique in computer science for exploiting vulnerabilities in computer programs due to erroneous assumption by designers.
  • Dependency injection, a programming design pattern and architectural model, sometimes also referred to as inversion of control
  • Fuel injection, a means of metering fuel into an internal combustion engine
  • SQL injection, a security vulnerability that occurs in the database layer of an application

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