Just an interesting little shot. Found this tool nicely placed on a sectioned off square of this odd looking plate, and illuminated it from beneath with a flashlight.

I found several of these small trays in an old medical building. After a little research, I learned that this was part of a complete tool called a Fisher Flo-thru hemophotometer. It was designed to produce a very accurate reading of the level of hemoglobin in a patients blood by injecting a sample between two moderately opaque plates, and calculating results via two beams of light that nearly cancel one another out, the remainder being read as the level of hemoglobin. I wish I could offer a more in depth explination (and hope this is mostly accurate), but the manual was ruined and very difficult to read.