You Look Through the
Optical Microscope at the Milk

Zack carefully draws a drop of milk from the bottle, and adds a series of chemicals to it. "Gram stain," he explains. "Sticks to the coats of bacteria. So you can see them better." He covers the milk with a thin plastic cover slip. "Have a look," he says, handing it to you.

The microscope is set at its highest magnification. You look through the eyepiece. As you study it for a while, you see organisms in the liquid. They seem to be composed of just one cell.

"Now here's a drop from Good Milk B," Zack says, handing you another slide. You spot more single-celled organisms almost immediately.

You place the two slides side by side, and Zack peers through the eyepiece. "Do they look the same to you?" you ask. "Hard to tell," he shrugs. "We'll test 'em both: Group MA and Group MB. 'M' for microscope." He takes both samples into the back room.

Continue investigating the biology lab

An Access Excellence Science Mystery sponsored by Genentech, Inc.