502 ANIMAL PHYSIOLOGY. 
now treat of the functions of a portion of the ear, according to 
our present classification. 
HAVE THE SEMICIRCULAR CANALS A CO-ORDINATING 
‘ FUNCTION ? 
Physiologists have as yet been unable to assign to the semi- 
circular canals a function in hearing, and upon certain results, 
partly of disease but chiefly of experiment, it has been con- 
cluded, though somewhat dubiously, that they are concerned 
with those sensations that conduce to or are essential to main- 
tenance of the sense of equilibrium; in a word, that they are 
the organs of that sense in the same way that the eye is the 
organ of vision. 
Experimental. When in a bird, as a pigeon, one of the mem- 
branous semicircular canals on one side is cut through, move- 
ments of the head, varying with the canal cut, result; though 
these are not permanent, when the operation is unilateral. 
After the bilateral operation a bird flies with difficulty, eats and 
drinks, but not as usual, and behaves generally in a way to in- 
dicate loss of co-ordination. It appears to be dizzy. It can hear 
well, and is not paralyzed, nor is there even weakness of the 
muscles. The phenomena in other animals, while not quite the 
same, indicate that the essential failure is in co-ordination of 
muscular movements. When the peculiar movements of the 
head or eyes, at first ensuing on operation, are permanent, it is 
possible that there may have been injury, either primary or 
secondary, to the cerebellum or other parts of the brain. There 
are very many ways in which giddiness and consequent inco- 
ordination may be induced in man and the lower animals. 
When this is brought about by rapid rotation, both the disturb- 
ance in the distribution of the blood within the cranium and 
actual displacement of brain-substance, or at least molecular 
disorder, must be at the bottom of the matter. 
In Meniére’s disease, vertigo is a prominent symptom in 
certain cases, but absent in others. Again, it is asserted that 
vertigo may be induced in animals in which both auditory 
nerves are divided. For our own part, we believe an undue im- 
portance has been attached to the semicircular canals in the 
present connection. Experiments on animals can not alone 
solve such problems as this, for the reason that we can never 
know, except in the vaguest way, their states of consciousness. 
Indeed, the latter must always be interpreted by our own, or 
