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Most of us have an overwhelming fear of injections in our childhood days. For most of us, that fear does not subside as we grow up. Apart from creating a phobia, there are many disadvantages of injections with needles such as they cause tissue damage. They could also act as a source of infection if the needles are reused or used incorrectly. 

Needle free injections were first described by Marshall Lockhart in 1936 in his patent jet injection. By the early 1940’s high pressured guns were developed that used a fine jet of liquid to pierce the skin and deposit the drug under the tissue.

Cryogenics is an advanced subclass falling under the refrigeration technology. So, let’s take a brief overview on refrigeration and air conditioning. It is basically about taking energy from a given volume (low temperature) and throwing it into the atmosphere (high temperature) but, according to the rules of nature it is impossible (at least without doing some work on the system). To prove this, we can simply prove the converse wrong.  In a glass of warm water place an ice cube, if energy is transferred from the low temperature object to the higher temperature, then that means the ice cube has to transfer some of its heat to the warm water, which would imply that the ice cube becomes colder and the warm water becomes hotter which as we could imagine is not what happens. So how do refrigerators keep cool objects cold?

It is achieved by smartly breaking down the energy transfer into smaller steps. First a cool refrigerant (which is cooler than the refrigerated space) is passed through the walls of the refrigerator. 

The first law of thermodynamics states, “Energy can neither be created nor destroyed, but can be converted from one form to another”. The first part of this law tells us that there is a fixed amount of energy in the universe whereas, the second part gives a sneak peak into how we can utilize the available energy to alter it into a form which is useful to us. The ideal case would be that the entire portion of the source energy be converted to the form of our choice.