False-colour transmission electron micrograph (TEM) of a Clostridium tetani bacterial spore. The bacterium causes tetanus (lockjaw). Here, a thick- walled endospore has developed with many membranes forming its coat (purple). This is a resting phase of the bacteria induced by adverse conditions, and the spore will germinate when conditions become favourable. C. tetani exists in soil and harmlessly in the intestine of man and domestic animals; it becomes pathogenic when introduced into a wound. The disease of tetanus, sometimes fatal, leads to painful muscle spasms & stiffness. Vaccination is effective. Magnification: x8, 500 at 6x7cm size.