Description: After a short historical introduction the anatomy of the carotid body is demonstrated on the dog. The histology of the carotid body and the anatomy of the aortic body is demonstrated by means of diagrams. A series of simple demonstrations of the functions of the chemoreceptors is then presented. The film is divided into sections Effects of Excess Carbon Dioxide, Effects of Changes in Hydrogen-ion Concentration, Effects of Oxygen Lack, Effects of Cyanide Injection, Electrical Stimulation of the Carotid Chemoreceptors and Chemical Stimulation of Aortic Body Chemoreceptors.