For instance, they were used to stain previously invisible microbes and bacteria, allowing researchers to identify such bacilli as tuberculosis, cholera, and anthrax.
In the lab, when doing a gram stain, Clostridium perfringens is Gram-positive, or purple when Gram stained, and look like big cylinders or rods, also called bacilli.
When doing a Gram stain, Clostridium tetani stains purple— or gram positive— and it's a bacillus, meaning that it looks like a big cylinder or rod under the microscope.