Sheep blood is added to growth media to enhance the nutrients available for bacterial growth.  Laboratory scientists grow various bacteria on this medium as well as numerous other media, in order to help assess infections in humans and animals.  The image on the right shows growth of a beta-hemolytic streptococcus. The bacterium has produced a hemolytic compound that has lysed the red blood cells surrounding each colony.  The plate was properly streaked to attain isolated colonies.  The plate on the left is growing a Staphylococcus species.  The plate was streaked too heavily, so isolated colonies were not attained.
Bill Branson – (Edited by <a href="//commons.wikimedia.org/wiki/User:Fir0002" title="User:Fir0002">Fir0002</a>)(Edited by <a href="//commons.wikimedia.org/w/index.php?title=User:Drhx&amp;action=edit&amp;redlink=1" class="new" title="User:Drhx (page does not exist)">Drhx</a>)
1985-10
This image was released by the <a href="https://en.wikipedia.org/wiki/National_Cancer_Institute" class="extiw" title="en:National Cancer Institute">National Cancer Institute</a>, an agency part of the <a href="https://en.wikipedia.org/wiki/National_Institutes_of_Health" class="extiw" title="en:National Institutes of Health">National Institutes of Health</a>, with the ID <a rel="nofollow" class="external text" href="https://visualsonline.cancer.gov/details.cfm?imageid=2230">2230</a> (<a rel="nofollow" class="external text" href="https://visualsonline.cancer.gov/retrieve.cfm?imageid=2230&amp;dpi=300&amp;fileformat=jpg">image</a>) <a class="external text" href="https://commons.wikimedia.org/w/index.php?title=Category:Media_from_National_Cancer_Institute_Visuals_Online_with_known_IDs&amp;filefrom=2230#mw-category-media"><small>(next)</small></a>.