Silent killer: Viewed this way it is not scary, indeed it even has something artistic, but behind this innocent appearance hides a killer who kills millions of women every year: it is a breast cancer cell under the microscope.
A cross section of a bundle of nerve fibers. Axons (orange) are wrapped in myelin (purple); an extension of the membrane of glial cells. Myelin has high lipid content, and acts to insulate the axons, causing them to transmit nerve impulses much faster.
The simplest life-forms on Earth have just one cell. An example of a one-celled life-form is a bacterium. These species of bacteria all cause diseases in humans. But many bacteria are not harmful, or even helpful.