Because the way our solar system works it only happens either yearly or just depends on the situations
Some samples are transparent, or very difficult to see, therefore, they are stained in order to be seen more clearly and easier to work with.
During eye surgery, the clear layer of the eye is stained to be easily extracted, if it was clear then the surgeon might cut the eye instead of just the layer.
Hope this helps, u might want to search online for more info.
The Gallbladder stores bile that is produced in the liver
Spinal cord is the part of the central nervous system which is used to serve as the main communication link between the body and brain
