Since bacteria are smaller than anything that can be seen by the human eye, identifying the genus and species of bacteria can be difficult. For identifying bacteria outside the body, two common chemical techniques are as follows. This technique is named after a pioneering Danish microbiologist. It works as follows.
Most bacteria are then stained red.
The bacteria are stained again with Potassium Iodide. The bacteria are then washed with alcohol. Those bacteria that retain the dye after washing are known as Gram Positive bacteria. Those that lose the dye are known as Gram Negative bacteria. Gram Negative bacteria will go pink after this dyeing, whereas Gram Positive bacteria will remain purple, from the original purple dye.