How does the Caloric Nystagmus Arise?

BARANY, as early as 1905, advanced the theory that the nystagmus, which appears by cooling and by heating in the external auditory meatus, is due to a movement of the cupula arising from a motion of the endolymph in the semicircular canals, especially in the lateral canal. The nystagmus is produced by the increased or diminished gravity of the fluid in its most exposed parts due to the change of temperature. This is a simple explanation of the contrary effect of heat and cold and also of the reversion of the caloric nystagmus by forward bending of the head. In the same way we can .thus explain why bending of the head towards the side irrigated with cold water gives a more horizontal nystagmus (sometimes a rotatory reversion is seen), while bending to the opposite side gives a more rotatory form of nystagmus (sometimes horizontal reversion). Bartels has controverted this explanation and has maintained that the cold water reaction is due to paralysis, the warm water reaction to irritation of the labyrinth in question. This theory, however, could not explain the dependence of the form and direction of the caloric nystagmus upon the position of the head, especially the reversion by forward bending. The theory, therefore, was exploded. Later on, several theories have been propounded, of which, however, Kobrak's is the only one which has met with a certain degree of sympathy. He thinks that heat and cold affect the vessels in the labyrinth in opposite ways and thus produce reactions having different directions. This view has been severely criticised by Grahe, neither does it, in my opinion, give a satisfactory explanation of the peculiarities of the reaction. In Denmark the subject was raised in 1920 by Borries. The fact that in certain pathological cases, only the caloric nystagmus, in other cases only the post-rotatory nystagmus, can be produced, gave him the idea that the former is released from the otolith organs and the latter from the semicircular canals. He considers that he has proved this by experiments on