31-MAY-1852 :- Birth Of Julius Richard Petri , Inventor Of Petri Dish.

Julius Richard Petri 
(May 31, 1852 – December 20, 1921) was a German microbiologist who is generally credited with inventing the Petri dish while working as assistant to pioneering bacteriologist Robert Koch.

Petri dishes are often used to make plates that are used for microbiology studies. The dish is partially filled with warm liquid containing agar, and a mixture of specific ingredients that may include nutrients, blood, salts, carbohydrates, dyes, indicators, amino acids and antibiotics. After the agar cools and solidifies, the dish is ready to receive a microbe-laden sample in a process known as inoculation or "plating." For virus or phage cultures, a two-step inoculation is needed: bacteria are grown first to provide hosts for the viral inoculum.

Often, the bacterial sample is diluted on the plate by a process called "streaking": a sterile plastic stick, or a wire loop which has been sterilized by heating is used to take the first sample, and make a streak on the agar dish. Then a fresh stick, or a newly sterilized loop, passes through that initial streak, and spreads the plated bacteria onto the dish. This is repeated a third, and sometimes a fourth time, resulting in individual bacterial cells that are isolated on the plate, which then divide and grow into single "clonal" bacterial colonies.

Petri plates are sometimes incubated upside down (agar on top) to lessen the risk of contamination from settling airborne particles and to prevent water condensation from accumulating and disturbing the cultured microbes.

Scientists have long been growing cells in natural and synthetic matrix environments to elicit phenotypes that are not expressed on conventionally rigid substrates. Unfortunately, growing cells either on or within soft matrices can be an expensive, labor-intensive, and impractical undertaking