Unit 8

Little Dish, Big Impact

by Taryn Perry, age 16

The Petri dish is an amazingly useful invention. However, with its simple design, it is easy to overlook. Far from insignificant, this dish has aided in many scientific studies from analyzing influenza to culturing scarlet fever in milk. This dish has revolutionized science by allowing scientists to sanitarily and efficiently analyze bacteria and other small creatures. Its design is simple. Its purpose is straightforward. Its impact is immense. How was this amazing dish created? Julius Richard Petri invented the Petri dish in 1877 in a microbiology lab. From then until its utilization in modern times, little has changed in this fascinating device’s purpose and model. What began as a great invention has remained just as impressive.

The inventor of this amazing little dish, Julius Richard Petri, was born May 31, 1852 in Barmen, Germany. Attending Kaiser Wilhelm Academy for military physicians, he studied medicine. For the final part of his training, Petri worked at Charite Hospital in Berlin as a military physician. In 1877 he transferred to the Imperial Health Office, where he was an assistant to Robert Koch, a microbiologist who ran the lab. Koch impacted him greatly. It was in this lab that Petri developed an interest for microbiology, which changed the course of his career. Generally he is remembered as a notable microbiologist with minimal emphasis placed on his time as a physician. Most noteworthy of all his accomplishments was his invention of the Petri dish. While working in Koch’s lab, Petri developed this incredible, important, pocket-sized dish.

Before the invention of the Petri dish, scientists used traditional test tubes and glass dishes to grow bacteria cultures. Because they were exposed to open air, however, they were not ideal. Later, it became customary to place a bell jar over a glass plate because this allowed scientists to view the cultures and spread them out over the plate. Unfortunately there was one problem: the bell did not fit under a microscope. In order to clearly view the bacteria, the bell had to be removed, which exposed the contents to contaminants. This led to erroneous experiments. Petri had the idea to place a slightly larger glass lid over a glass dish. The large surface area aided in bacteria growing and streaking—the process of spreading cultures for more accurate experimentation—while the flat glass allowed for better viewing. In addition, the simple but ingenious design made it easy to clean and therefore sanitary. Most importantly, the dish was thin enough to fit under a microscope without requiring the removal of its lid. Termed Petri dishes, these glass containers continue to be an excellent way to culture bacteria, free from contaminants.

A Petri dish is made by placing a slightly larger lid over a glass or plastic dish. Since the dishes are thin, they fit under a microscope without the removal of the lid. Filled with bacteria cultures, Petri dishes are used to grow, isolate, and examine cultures of bacteria, pathogens, microbes, or protozoa. In microbiology, the dishes are filled with agar and termed “agar plates.” Agar is a jellylike substance, indigestible to many microbes. Consequently it provides a stable base on which bacteria can be cultured. Before the dish is carefully filled, the agar is mixed with blood, carbohydrates, nutrients, antibiotics or amino acids. Cultured atop the agar, microbes feed off of the substances mixed into it. Scientists are then able to analyze and effectively, efficiently experiment on bacteria cultures as they raise them in a simple dish.

While the Petri dish is still used in microbiology, its uses have entered many diverse and complicated fields around the world as well. Current uses include eukaryotic cell culturing, lab storage, agar plate making, and plant growth. A few modifications have been made, although the dishes remain similar to Petri’s original. One main difference is that they are now made of disposable plastic rather than glass. Mass-produced on plastic molding machines, the dishes can be made rather cheaply. Once an experiment is over, and before they can contaminate other areas, the dishes are disposed of, keeping subsequent cultures from being ruined. Also, the dishes are sterilized by gamma radiation or ethylene gas before being sent to labs. The process is similar to thoroughly heating tools to sanitize them. Not surprisingly, the efficiency provided by Petri dishes has aided in scientific discoveries in many fields, without needing much modification.

Although the Petri dish seems rather simple, it is truly amazing. Emerging from Petri’s experiences under Koch, this invention is now used around the world. Petri dishes have revolutionized science and aided in many discoveries. Of all the benefits of the Petri dish, its straightforward, efficient, and ingenious design, which has been modified little, makes it practical. Unfortunately this invention is often overlooked or taken for granted because of its simple design. However, Petri dishes are extremely useful and their benefits in the scientific realm are undisputable.

“Julius Richard Petri.” Wikipedia. Wikimedia Foundation, n.d. Web. 08 Mar. 2016.
“Julius Richard Petri – Isolation of Bacteria.” LumiByte. LumiByte, n.d. Web. 08 Mar. 2016.
“Science Diction: The Origin of the Petri Dish.” Interview by Ira Flatow.NPR. NPR, 16 Dec. 2011. Web. 08 Mar. 2016.
“World of Microbiology and Immunology on Richard Julius Petri.” BookRags. BookRags, Inc., n.d. Web. 08 Mar. 2016.
Hardy, Jay. “Petri’s Famous Plate.” Hardy Diagnostics. Hardy Diagnostics, 30 June 2011. Web. 8 Mar. 2016.
Signh, Anoopa. “How Julius Richard Petri’s Dishes Changed Medical History.” Medical Daily. IBT Media Inc., 31 May 2013. Web. 8 Mar. 2016.

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