Google celebrates 166th birthday of Danish microbiologist Hans Christian Gram with a doodle. The art is beautifully designed and illustrated by Danish guest artist Mikkel Sommer. He is noted for his the development of the Gram stain – the first step in the preliminary identification of a bacterial organism. The Doodle art features everything from Gram’s experiment to a closer look of a microscope and bacteria samples.

The work that gained Gram an international reputation was Hans Christian Gram’s development of a method of staining bacteria, to make them more visible under a microscope. The stain later played a major role in classifying bacteria.

Gram was a modest man, and in his initial publication he remarked, “I have therefore published the method, although I am aware that as yet it is very defective and imperfect; but it is hoped that also in the hands of other investigators it will turn out to be useful.”

According to Google, Gram travelled through Europe studying bacteriology and pharmacology after earning his M.D. from the University of Copenhagen in 1878.

Gram published his findings in a scholarly journal in 1884, and the terms “Gram-positive” and “Gram-negative” came to be coined.

A Gram stain is made using a primary stain of crystal violet and a counterstain of safranin. Bacteria that turn purple when stained are called ‘Gram-positive’ because their cell walls are so thick that the solvent cannot penetrate them. While those that turn red when counterstained are called ‘Gram-negative’ because they have thinner cell walls that allow the solvent to wash away the stain.

In his publication, Gram had notably included a modest disclaimer: “I have therefore published the method, although I am aware that as yet it is very defective and imperfect; but it is hoped that also in the hands of other investigators it will turn out to be useful.”

This simple test, however, proved widely applicable. Gram’s staining method continues to be used today, more than a century later.

Happy Birthday, Hans Christian Gram!