In the upper right corner of the game window, you will find a "help" section with instructions and hints for playing the game. But if that isn't enough, this walk through should help you.

1.
Pick up the methylene blue dye and the vesuvian brown dye from the table by moving the mouse cursor on top of them and clicking on the "hand symbol."

2.
Pick up the slides on the table in the same manner.

3.
Follow Wilma through the door to the left of the cages and pick up the expectorant sample on top of the shelf. The items will be placed in the inventory that you can reach in the upper right corner of the game window.

4.
Click on the expectorant sample in the inventory and drag it on top of the slide in the inventory. Click again to release the sample, which places it on the slide.

6.
Click on the methylene blue dye in the inventory and drag it on top of the slide. Click again to release the dye, which places it on the slide.

8.
After clicking anywhere in the game window, you can read four short pages about Koch's staining technique. Use the orange arrows to go forward and then click on the "Back to game" button.

9.
Go back to the room with the microscope by moving the mouse cursor onto the door and clicking on the "hand symbol." Click on the slide in the inventory and drag it on top of the microscope. Click again to release the sample, which places it under the microscope.

11.
Click on the expectorant sample in the inventory and drag it on top of the culture plate on the table. Click again to release the sample, which places it on the culture plate.

13.
Now you are able to enter the door to the left of the sink.

15.
Catch the guinea pigs by clicking on them with the mouse cursor.

16.
After reading Koch's Postulates, click on the "Continue" button. After a few more text pages you can continue by clicking on the "Back to game" button.