The is the same subject shown in the previous image, except that it is immersed in alcohol. Although water can also be used, alcohol is easier to work with. Since tissue has a higher specific gravity than alcohol, the subject won't float to the top of the liquid. Also, tiny bits of tissue, which would float around in water and cloud the image, sink right to the bottom and stay out of the way. This makes alcohol seem "clearer" than water.
Source: Ed Uthman, MDOriginal file here.