788 THE SENSE OF EQUILIBRIUM 



is again able to fly and to walk, although it continues to suffer from a 

 certain loss of tonus of its muscles, principally of those of the head and 

 trunk on the side opposite to the injury. 



The destruction of the canals on the two sides gives rise at first to 

 a complete loss of equilibrium, so that the animal can neither walk nor 

 fly unless supported. It tends to assume a quiet attitude, but when 

 made to move, executes violent forced and incoherent movements 

 which may even cause its destruction. Its muscles are abnormally 

 flaccid and the joints unusually limber. So small a weight as 20 

 grams attached to its bill or neck, suffices to keep the head perma- 

 nently in the most abnormal position, and to make it sway in the direc- 

 tion of the weight. These disorders gradually disappear in the course 

 of a few weeks. The animal learns to walk again by making use of the 

 sensations of sight and touch. The muscular weakness, however, 

 persists and losses of equilibrium may be brought about at any time 

 later on by bandaging the eyes. 



These defects may be localized and restricted to single planes of the 

 body by destroying only one of these canals. Thus, the loss of, say 

 the horizontal canal, invariably causes the pigeon to make forced 

 movements of the head in the horizontal direction, but any unusual 

 excitation immediately leads to more general rotary movements of the 

 entire body. The length of time during which these symptoms remain 

 in evidence, depends upon the location and extent of the lesion; at 

 all events, it does not suffice to destroy solely the bony canal or to let 

 the perilymph escape through a fistulous opening. These defects are 

 quickly compensated for, provided the membranous canal is left intact. 

 Decided symptoms can only be produced by opening the latter widely 

 and as close to the ampulla as possible. 



The destruction of the labyrinth in amphibia is followed by symp- 

 toms which are very similar to those just enumerated. Thus, its 

 removal on one side causes the animal to tilt its head and to move 

 about in a circle toward the injured side. Moreover, when this animal 

 is placed upon its back, it experiences great difficulty in righting itself, 

 and when made to swim, frequently executes rotary movements 

 toward the operated side. Its musculature exhibits a decided loss of 

 tonus and precision of action. Disorders of a very similar kind are 

 exhibited by mammals after the destruction of one or more sets of 

 semicircular canals. 



The Effects of Stimulation of the Semicircular Canals. — Ewald^ 

 has succeeded in rendering certain canals functionally useless by 

 opening their bony wall with a dentist's burr and temporarily com- 

 pressing their membranous tube by means of a plug of amalgam, but 

 the disorders in the plane of this particular canal were evinced only 

 after the corresponding membranous tube on the opposite had also 



1 Physiol. Untersuchungen iiber das Endorgan des Nervus octavus, Wiesbaden, 

 1892; also: Schrader, Pfliiger's Archiv, xli, 1893, 75. 



