The answer is cholesterol
This process is called Melting.
There are three physical types of media, theses are solid, liquid and semi-solid.
In liquid media, growth occur throughout the media. In solid media, there are firm surfaces for bacteria to form discreet colonies. This type of media usually contain 1-5% agar. For semi-solid media, this type of media has soft constituency at room temperature and does not flow freely.
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