Jet injector
A jet injector is a type of medical injecting syringe that uses a high-pressure narrow jet of the injection liquid instead of a hypodermic needle to penetrate the epidermis. It is powered by compressed air or gas, either by a pressure hose from a large cylinder, or from a built-in gas cartridge or small cylinder. Some are multi-shot, and some are one-shot. They are made in various shapes, as the links to images below show.
They are used by diabetics to inject insulin as an alternative to needle syringes, though they are still not very common.
In the Star Trek franchise, and sometimes in other fictional scenarios and occasionally in the real world, it is called a hypospray.

# Types of jet injector

## Jet Injectors
The Jet Injector Gun and the Ped-O-Jet are air-powered medical injector devices designed to administer vaccinations in an extremely efficient manner. Invented by Aaron Ismach, these medical devices were bought in mass quantities by the US Government and provided to governments around the world to eradicate smallpox and other diseases.  Servicemen in the Armed Forces were routinely injected with these medical devices to immunize them, and civilian usage included vaccinations during flu epidemics and the like.  The Jet Injector is powered by electricity, while the Ped-O-Jet version is powered by a foot pump and does not require electricity to administer the vaccines. These devices has various specialized nozzles for different medication densities and also permitted the efficient inoculation of animal populations as well.
The Biojector 2000 is a make of gas-cartridge-powered jet injector. It is claimed that it can deliver intramuscular injections and subcutaneous injections up to 1 milliliter. The part which touches the patient's skin is single-use and can be replaced easily. It can be powered from a big  compressed gas cylinder instead of gas cartridges. It is made by Bioject.
In October 2006 it was in clinical trials for patients using Fuzeon as part of their HAART treatment for HIV. For clinical trial and related information see 

# History
- 19th century: Workmen in France had accidental jet injections with high-powered grease guns 
- 1920s: Diesel engines begin to be made in large quantities: thus beginning of serious risk of accidental jet-injection by their fuel injectors as workshop accidents.
- 1937: First known recorded accidental jet injection by a diesel engine's fuel injector.
- 1960: Aaron Ismach invented and patented the Jet Injector medical device which was used for quick mass vaccination of smallpox and other diseases.  Ismach was assisted by Dr. Abram Benenson in the development of the Jet Injector Gun. The new method met with tremendous success as teams vaccinated large numbers of people at collecting points in the affected countries. The foot operated gun was called the Ped-O-Jet and the electric operated gun was called the Jet Injector Gun.
- 1962: Robert Andrew Hingson claimed to have invented a prototype jet injector and called it the peace gun, for quick mass vaccination. But sometimes the injection process dislodged infected matter from a patient onto the nozzle of the injector, risking cross-infection.
- 1964: Aaron Ismach was presented with a Gold Medal from the US Government for his efforts related to the Jet Injector Gun.  The Jet Injector also appeared on postage stamps as a commemorative of his efforts.
- September 1966: The Star Trek series started, exposing the public to the idea of jet injectors under the name "hypospray".
- 1976: The USA Agency for International Development published a book called War on Hunger which detailed the War Against Smallpox which Ismach's Jet Injector gun was used to eradicate the disease in Africa and Asia.  The US Government spent $150 million a year to prevent its reoccurance in North America.
- 1997: The USA Department of Defense, the jet injector's biggest user, announced that it would stop using it for mass vaccinations due to concerns about infection.