In the vestibular labyrinth of mammals there are five separate end-organs, the cristae of the three semicircular canals and the maculae of the utricle and saccule. These end-organs normally react to mechanical stimulation, the cristae to rotatory acceleration, and the maculae to linear acceleration and to gravity. By using natural stimuli, however, it is difficult to selectively stimulate single receptors.

Since experiments utilizing single organ stimulation are frequently of interest, a variety of techniques have been devised to accomplish this purpose. Ewald! used a pneumatic hammer connected to a small catheter to stimulate single semicircular canals of pigeons. Lorente de N62 heated individual semicircular canals of rabbits with a hot needle. Szentagothai" introduced catheters directly into semicircular canals of dogs, and also stimulated the utricular macula with a probe.'Anderson and Cernandt," Fluur," Szentagothai," and others?" have used electrical stimulation for activating single ampullary or otolithic nerves in acute experiments.