English: This image depicts a view of a Petri dish culture plate, which contained a growth medium of sheep blood agar (SBA), and which had been inoculated with Bacillus anthracis. In this case, what you’re seeing is a positive result of what is known as a phage test, whereupon, you’ll note the diminished growth (circular area) contained within the confluent colonial growth, known as oval-shaped macroplaque, where a gamma phage suspension had been applied atop the blood agar medium. This particular culture was incubated in a carbon dioxide-free environment, at a temperature of 35 °C.