What is the purpose of a mounting medium in biology?

Using a mounting medium is important when you want to observe a specimen under a microscope. The mounting medium serves several important purposes: 

• Helps hold the sample in place while you are imaging. 
• Mechanically stabilizes and supports the sample so delicate structures don’t break off. 
• Prevents the sample from drying out. 
• Prevents moisture and bacteria from coming in contact with the sample, causing it to decompose. 
• Reduces photobleaching 
• Improves image quality when its refractive index (RI) closely matches the RI for the objective you will use
• Preserves sample for long-term storage