A system is provided that is useful for hypodermic injection of medication without piercing the skin with a needle. The system includes a gas pressure actuated needleless hypodermic injection device for injecting medication through the skin. The injection device includes an injector assembly having an...http://www.google.com.hk/patents/US5024656?utm_source=gb-gplus-share專利 US5024656 - Gas-pressure-regulated needleless injection system
