114 



NA TURE 



[June 4, 1908 



range is only li inches at Dululh and one-lhird inch a^ 

 Marquette. 



In Appendix No. 7 is given a detailed description, with 

 appropriate illustrations, of the long wire drag, a device 

 for detecting erratic obstructions of small extent in 

 navigable waters. The method of operating can be under- 

 stood from the simple statement that the drag is a wire 

 varying in length from 4S0 feet to 1400 feet, supported at 

 suitable intervals, and maintained at any desired depth 

 below the surface of the water. This drag is towed over 

 anv given area by launches, and in the -area so searched 

 no elevation of the bottom above the depth at which the 

 wire is suspended can escape detection. Buoys floating 

 at regular intervals along the drag indicate to observers 

 in the launches when and where an obstruction is touched, 

 and the spot so indicated is then accurately determined. 



This method of sweeping has proved a sure means of 

 detecting pinnacle rocks and similar erratic obstructions 

 which heretofore have eluded the hydrographlc surveyor, 

 since it is almost impossible to discover them by lines of 

 soundings with the lead. Only the navigator in whose 

 hands rest many lives and much property can realise the 

 relief from mental strain that comes from knowing that 

 the water in which he is sailing is absolutely free from 

 hidden dangers, or that every menace is charted. The 

 device has proved very satisfactory under widely varying 

 conditions, and marks a decided advance in marine 

 surveying. 



The report, or any one of the appendices, may be 

 obtained by interested persons, free of charge, upon 

 application to the superintendent of the Coast and Geodetic 

 Survey, Washington, D.C., U.S.A. 



THE MECHAXICS OF THE INNER EAR. 

 'T'HE University of Missouri has recently issued a 

 memoir by Prof. Max Meyer, in which an interest- 

 ing, instructive, and suggestive attempt is made to explain 

 the mechanism of the cochlea without having recourse to 

 the application of the principle of sympathetic vibration, or 

 rather without the assumption that there exists in the 

 cochlea, in the form of the organ of Corti, a vast number 

 of delicate structures tuned, as it were, to tones of different 

 frequencies. Prof. Max Meyer does not base his views on 

 experimental data ; his paper is a purely theoretical dis- 

 cussion as to how the cochlea may act, if we make six 

 fundamental assumptions, none of which can, at present 

 at all events, be tested by direct examination or bv direct 

 experiment. His inquiry begins with the movements, in 

 and out, of the stapes at the oval window. The tube filled 

 with fluid is divided into three compartments, the upper, 

 the scala vestibuli, communicating at the apex of the 

 cochlea with the scala tympani, at the foot of which we 

 find the round window, while between the two scala; we 

 have the cochlear duct, or scala intermedia, composed, in 

 its turn, on one side by the basilar membrane, on which 

 rests the organ of Corti, and on the other by Reissner's 

 membrane. When the base of the stapes is pushed 

 inwards at the base of the scala vestibuli, pressure is com- 

 municated to the fluid in the scalse (the scalae communi- 

 cating at the apex of the cochlea by a little opening, 

 the helicotrenia), and the membrane of the round window 

 passes outwards, towards the tympanic cavitv. It is 

 generally held that with such pressure the fluid in the 

 scalae moves as a whole, and that pressure is communi- 

 cated to the whole length of the scala intermedia, and 

 especially to the basilar membrane, and that in this way 

 the nerve-endings in Corti 's organ are also submitted to 

 pressure. The question then arises, is there any differ- 

 entiating mechanism in the basilar membrane or in 

 Corti's organ for tones of different frequencies, or, in other 

 words, have we here an organ capable of analysis? Some 

 deny any such property, while others, since the views of 

 Helmholtz were first promulgated, are of opinion that there 

 does exist an analysing mechanism. 



The theory of Prof. Meyer essentially is that when the 

 base of the stapes is pressed inwards a section of the 



' " *" Introduction to the Mechanics of the Inner Ear." By Prof. Max 

 Meyer. Science Sfries of the University of Missouri Studies. Pp. 140. 

 (1907.) Price I dollar. 



NO. 2014, VOL. 78J 



membrana basilaris is also pressed in one direction until 

 it reaches its limit of movement. On the basilar membrane 

 rests the organ of Corti, the delicate hair cells being 

 supported on the backs of the rods or arches of Corti. 

 The membrane of Reissner may be regarded as merely 

 protective, and a similar function Prof. .Meyer awards to 

 the arches of Corti, which are a kind of skeleton to 

 prevent the delicate hair cells and nerve endings from 

 being crushed by downward pressure on the membrana 

 basilaris. No one can say what is the function of the 

 membrana tectoria, the cushion-like structure that lies over 

 the apices of the hair cells, and the nerve endings that, 

 according to some histologists, lie between the hair cells. 

 It may be a damper or it may be the arrangement by 

 which pressures are made on the apices of the hair cells 

 or nerve endings. There is thus, according to Prof. 

 Meyer, a movement in one direction of a segment of the 

 inembrana basilaris, the direction being towards the scala 

 tympani. When the base of the stapes has passed inwards 

 to its fullest extent, the segment also moves to its limit, 

 and then when the base of the stapes passes outwards 

 the segment passes in the reverse direction, that is, towards 

 the scala vestibuli. The rest of the basilar membrane 

 beyond the segment is undisturbed. It is not known 

 whether the basilar membrane is elastic or not ; most prob- 

 ably it is non-elastic, but its backward swing has also its 

 limits, and the velocity of the backward spring is probably 

 slower than its forward swing, seeing that it is weighted 

 on one side by the Corti cells, &c. The intensity of the 

 lone will be determined by the amplitude of movement of 

 ihe base of the stapes — the extent of the segment being 

 greater as the amplitude is greater, and the reverse. 

 Assuming that the number of nerve fibres in each segment 

 is the same (which is unlikely), the greater the extent of 

 i-he segment the greater will be the number of nerve fibres 

 irritated, and the greater will be the intensity. The pitch 

 >vill, of course, depend on the frequency of the movement 

 of the segment, and there is no necessity for the assump- 

 tion that either segments of the membrana basilaris, or 

 structures upon these, are tuned to certain frequencies. 

 When a compound tone or sound, say a fifth (the fre- 

 quencies of the components of which are in the ratio of 

 3 : 2), is sounded, the base of the stapes makes a more 

 complicated movement than that of a simple pendular 

 vibration, and then this compound movement is resolved 

 by two segments of the basilar membrane moving 

 synchronously, in the ratio of 3:2, and the nerve endings 

 in one segment would be irritated thrice during the time 

 that the nerve endings in the other segment would be 

 irritated twice. Still more, a segment at or near the base 

 of the stapes would move once in the same time, and give 

 rise to the differential tone, and so on. 



Prof. Meyer thus recognises the cochlea as an analytic 

 apparatus, without the necessity of any tuned mechanisms, 

 and he works out his theory with great clearness, much 

 ingenuity, and perfect fairness. His explanations of differ- 

 ential tones are in perfect consistence with his theory, and 

 they are graphically delineated. He does not pretend that 

 his theory is an ultimate solution of the problem attacked. 

 Data are still wanting to found a final theory, and when 

 we consider the minute size of the parts involved, it will 

 probably be many a day before these data have been 

 collected. But as experimental, and even observational, 

 research must start from theory, however imperfect. Prof. 

 Meyer has done good service in advancing his views. 



The writer would only remark that he finds it easier to 

 conceive the existence in the cochlea of arrangements 

 adapted to frequencies, and consequently of an analysis 

 by resonance, than to think of the membrana basilaris, 

 sfiort as it is, moving in segments when a complex mass 

 of tones is objectively produced. Such a cochlea as Prof. 

 Meyer has conceived might work in the way he thinks, 

 and the writer would suggest that he should make a huge 

 model, with a big piston, and ascertain whether a stout 

 leather non-elastic membrana behaves as he e.xpects it to 

 do. The writer thinks that Helmholtz's resonance theory, 

 with slight modifications, still holds the field, nor does it 

 seem to him to be negatived (and the same remark applies 

 to the theory of Prof. Meyer) even by the difficulties created 

 by a consideration of differences of phase. The physio- 

 logical effect produced by the relative intensity of a com- 



