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.
With DNA and small samples of organisms they are often transparent or very difficult to see. When you are viewing samples with a microscope the samples are so small that they are near about invisible to see as they are about half a micrometer thick or at times even smaller. The sample is placed in paraphin or epoxy, allowed to harden and then cut by a glass or crystal knife. The samples are then stained and placed under a microscope for viewing. The staining process can produce brilliant and beautiful designs from the crosssamples of these organisms.
