634 



NATURE 



{Oct. lo, 1878 



and to a crescent-shaped ridge, the crista acustica, near the 

 middle of each ampulla. The nerves in each case end in hair 

 cells the hairs of which project into the endolymph. These 

 nerves are derived from the vestibular branch of the so-called 

 auditory nerve, or portio mollis of the seventh pair. 



The remarkably regular, and, if we may use the expression, 

 purpose-like arrangement of these organs must strike every one, and 

 the mind naturally searches for the use of this curious geometrical 

 apparatus. A theory long held, and not yet wholly abandoned, 

 to which indeed Dr. de Cyon seems to attach some value, con- 

 nects it with the perception of the direction of sound. The idea 

 is not unnatural, and is obviously derived from the nearness of 

 the apparatus to the organ of hearing and from the relation of 

 its form to the three dimensions of space. No explanation has 

 ever been given hcrw it can serve this purpose, and a sufficient 

 proof that it does not do so is supplied by the fact — easily tested 

 by any one — that we have no means of knowing the direction of 

 sound except by two or more simultaneous or successive obser- 

 vations. If a sound is heard louder in the right ear than in the 

 left we conclude that it comes from the right, and by turning the 

 head round we quickly obtain a sufficient number of obser- 

 vations to enable us to judge of the exact direction. If a sudden 

 abrupt noise is made at a point equidistant from the two ears, we 

 do not know its position unless we see what produces it. This 

 theory may therefore be at once dismissed. 



The first scientific inquiry into the fimction of the semicircular 

 canals was made by Flourens in 1828. His experiments were 

 conducted with an amount of care and the results described with 

 a degree of accuracy and clearness not surpassed by any recent 

 investigator. He observed that the section of a membranous 

 canal was always followed by movements of the head, or even 

 of the body of the animal in the direction of the divided canal ; 

 in other words, by oscillatory movements of rotation about an 

 axis at right angles to the plane of the divided canal. 



Flourens has been followed by various observers, Harless, 

 Czermak, Brown-Sequard, Vulpian, and Lbwenberg, who have 

 confirmed the results above described, and referred them either 

 to disturbances of hearing or to injury of the cerebellum. 

 • An entirely new step was taken in 1870 by Prof. Goltz. 

 Flourens had already hinted that the semicircular canals are 

 concerned in the co-ordination of movements, but Goltz first 

 devised a physical theory to explain how they act in this way. 

 This theory may be called the statical theory, and is, shortly 

 stated, as follows : — We may suppose that the terminations of 

 the nerves in the ampullae are stimulated by pressure or by 

 stretching, as is the case with the nerves of the skin. The 

 endolymph contained in the canals necessarily presses most upon 

 that part of the wall of the cavity which is situated at the lowest 

 point, and each position of the head will correspond to a par- 

 ticular distribution of pressure, and therefore to a particular 

 form of nerve stimulation; we have thus a special sensation 

 corresponding to each position of the head. That a knowledge 

 of the position of the head and the power of regulating it is 

 necessary for the preservation of the equilibrium of the body, 

 was proved by Goltz by a very ingenious experiment. He fixed 

 the head of a pigeon in an unnatural position by attaching its 

 occiput to its breast, so that its beak was tiu-ned up and 

 the vertex looked forward. He found that the animal so 

 treated walked with great difficulty, and was quite unable to 

 fly, and exhibited many of the phenomena observable in animals 

 whose semicircular canals had been cut or destroyed. 



The next investigations of importance as to the function of 

 these organs are those of Prof. De Cyon in 1872. He re- 

 peated with great experimental skill, and with ingeniously- 

 contrived modifications, the operations performed by Flourens 

 and by Goltz, obtained the same results, and, guided by his 

 medical observations on diseases accompanied by loss of equili- 

 brium, formulated his theory as follows : — The semicircular 

 canals give us a series of unconscious sensations as to the posi- 

 tion of our heads in space ; each canal has a strictly determined 

 relation to one of the three dimensions of space ; the loss of 

 equilibrium and the other disturbances of locomotion caused by 

 the section of the canals are solely due to the disorder of these 

 sensations. 



Before considering the next step in the development of the 

 theory we must go back and examine the experiments on vertigo 

 made by Purkinje about the time when Flourens first investi- 

 gated the function of the semicircular canals. 



Every one knows that if we stand up and turn round about a 

 vertical axis and keep up this rotation for some time and then 



, stop, we see, or think we see, surrounding objects moving 

 i round. Purkinje studied the conditions under which this appa- 

 rent rotation occurs, and arrived at the following conclusions, 

 which have been confirmed by all succeeding observers : — i. 

 That the direction of the apparent motion of surrounding 

 objects depends upon the direction of the preceding real 

 motion of our body, and is always opposite to it. 2. 

 That the axis about which the apparent motion takes 

 place is always that line in the head which was the 

 axis of the preceding real rotation. Thus, if we turn round 

 with our head bent forward so as to look straight down at the 

 floor, and then stop, keeping the head in this position, the 

 apparent rotation takes place about a vertical axis ; but if, when 

 we stop, we lift up our head and look forwards, the apparent 

 rotation takes place about a fore and aft axis, the fore and 

 aft axis having been vertical while the real rotation occurred. 

 A trick, illustrating this principle, is sometimes played on per- 

 sons ignorant of this law of giddiness. They are asked to take 

 a poker in their hand, plant it vertically on the floor in front of 

 them, bow do\vn so as to touch the end of the poker with their 

 forehead, and walk quickly three or four times round the poker, 

 then rise up and walk to the door. The apparent rotation takes 

 place about a fore and aft axis, because the fore and aft line in 

 the head was the axis of the real rotation ; they see objects rise 

 up on the one side and fall down on the other ; the floor seems 

 to incline itself to one side, and equilibrium becomes impossible. 

 This experiment may be varied in many ways : thus, instead of 

 the forehead, one ear may be placed on the end of the poker ; 

 the rotation then takes place about a right and left axis — the 

 line from ear to ear. On rising, apparent rotation occurs about 

 this line as an axis, and the floor in front seems to slope up or 

 down according to the direction of the original real rotation. 



Purkinje explained these phenomena thus: — "During the 

 rotation of the body about its longitudinal axis, the brain, in 

 virtue of its soft consistence, ought to have a tendency to remain 

 a little behind the movement of the walls of the skull. This is 

 the same phenomenon which we observe in a liquid when the 

 vessel containing it is set in rotation. The particles of the 

 liquid preserve their position relative to the external space, until 

 their adhesion to the walls of the vessel forces them to take part 

 in the motion of the latter. The cohesion of the brain is too 

 great to allow of the reproduction of the same phenomenon 

 exactly ; but as the brain is soft and capable, to a certain extent, 

 of internal displacement, it has some of the properties of liquids. 

 We must therefore admit that a movement more or less intense 

 must produce a displacement and relaxation of its parts, although 

 an actual rupture of continuity cannot occur. Such distortions 

 should produce the same disturbances as actual mechanical 

 lesions, and differ from them only in degree." 



ITiis explanation is adhered to, in the main, by Dr. de Cyon, 

 and although we do not admit that such tortional deformation of 

 the brain is the chief or usual physical cause of the giddiness 

 above described, it is probable that it has something to do with 

 the phenomena when the rotation is very rapid and is suddenly 

 stopped. 



We now come to the modification of the theory of Goltz, 

 which induced Dr. de Cyon to resume his experiments on 

 the semicircular canals. This modification was made nearly at 

 the same time by Prof. Mach, of Prague, Dr. Breuer, of Vienna, 

 and Dr. Crum Brown, of Edinburgh. The papers in which 

 they stated their views were written independently, and were 

 published in the order above-mentioned within a period of about 

 six weeks. 



The views of the three observers are not quite identical, and it 

 wUl be necessary to point out in what they differ ; but they agree 

 in so many details that a general description of their theory is 

 possible. We have above called Goltz's theory statical ; in 

 opposition to it we may call the Mach-Breuer-Brown theory 

 kinetical, 



Goltz regarded the semicircular canals as organs which, by 

 difference of pressure in different parts of the system, give us a 

 notion of the aspect of the head in space. Mach, Breuer, and 

 Brown regard them as organs which, by virtue of the inertia of 

 the contained liquid and movable soft parts, give us a notion of 

 the change of aspect of the head. 



The simplest form of this theory is that in which it is stated 

 by Dr. Breuer : — 



*' In a system of three ring-shaped tubes, approximately at 



right angles to one another, and filled with liquid, as is the 



j case in the semicircular canals, there are produced by every 



