Today, Google Doodle is celebrating 166th birthday of Danish microbiologist Hans Christian Gram. He was born in Copenhagen on this day in 1853. The Google Doodle art is illustrated by Danish guest artist Mikkel Sommer.

Hans Christian Gram is known for his development of the Gram stain, which was was a groundbreaking discovery in the study of microbiology. He devised a staining technique that is now still used to identify and classify different types of bacteria. It makes the bacteria more visible under a microscope.

In 1878, Gram did his M.D. from the University of Copenhagen. After which, he traveled through Europe studying bacteriology and pharmacology. “While working in the lab of German microbiologist Karl Friedländer, he noticed that treating a smear of bacteria with a crystal violet stain, followed by an iodine solution and an organic solvent, revealed differences in the structure and biochemical function of various samples,” wrote Google on its blog.

Gram published his findings in a scholarly journal in 1884, and the terms “Gram-positive” and “Gram-negative” came to be coined. The Gram stain is essentially made using a primary stain of crystal violet, while the counterstain of safranin. “Gram-positive bacteria appear purple under a microscope, because their cell walls are so thick that the solvent cannot penetrate them, while Gram-negative bacteria have thinner cell walls that allow the solvent to wash away the stain.”

Who was Hans Christian Gram? (Google Doodle)

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.”

More than a century later, the simple Gram staining method is still used today to identify and classify different types of bacteria.