False-colour transmission electron micrograph (TEM) of Corynebacterium diphtheria, showing a number of the Gram positive, non-sporing, aerobic bacilli (rod- shaped bacteria) which are the causative agents of diphtheria. C. diphtheria is an obligate human parasite - man is its only natural host - and causes an infection of the upper respiratory tract. Other effects arise from the production of an exotoxin which enters the bloodstream and damages the heart, nervous system, liver, kidneys and adrenal glands. The bacilli are slightly curved, and their appearance has earned them the name of chinese characters". Magnification: x12,000 at 35mm size."