RYERSON PHYSICAL LABORATORY, UNIVERSITY OF CHICAGO

Communicated by R. A. Millikan, June 3, 1921

By means of the audion oscillator, a special telephone receiver tuned to a high natural period and placed against the ear and a suitable circuit numerous tests at various frequencies have been made on the minimum audibility current for both normal and abnormal ears. From these data important conclusions can be drawn regarding the physical and physiological structure of the ear and also concerning the functioning of the ear and the auditory nerves with their endings as organs of hearing. The conclusions drawn, then, are based on precise physical measurements which can be checked to within about five per cent from time to time.

Sensitivity of Normal Ears.-Ears are considered normal when no physiological defects are observable by the otologist. If we define sensitivity as the reciprocal of the minimum vibrational energy in ergs of the receiver diaphragm that the normal ear can detect, then curves can be plotted showing the sensitivity as a function of the frequency. This has been done for a number of normal ears. The curve shown in figure 1 is a typical one. It is to be observed that up to about 6000 cycles three distinct maxima of sensitivity are present; one at 900 cycles, one 1800 and another one at 3900. It is also important to observe that the sensitivity is much greater throughout the region from 200 to 4500 cycles than outside this range. Within this region are included all the frequencies which are of most importance for both speech and music. The natural period of the receiver was 5215 cycles when this curve was taken and the absence of a peak in this position shows that the receiver characteristics have been corrected for satisfactorily. All the maxima, then, occur below the resonant frequency of the receiver. Curves on other normal ears show maxima which agree for the most part in location but not in magnitude with the curve shown in figure 1. Because of the marked similarity between the response curves for coupled mechanical vibratory systems and the curves for normal ears, it seems

as though we are justified in thinking of the ear as whole as a coupled vibratory system and referring to the maxima of sensitivity as its resonant frequencies. The resonant frequencies are not to be thought of as harmonics of the fundamental.

Sensitivity of Abnormal Ears.-In the study of abnormal ears, where disease has affected certain portions of them and has produced partial deafness, curves of two types are plotted. The first type shows at the various frequencies how much current must pass through the receiver for the patient to just hear the tones compared with that required for a normal ear to hear. The second type shows the sensitivity of the ear at the various frequencies. Both methods of plotting the data are of value for studying the physical characteristics of the ear.

In figures 2 and 3 are shown curves relative to the normal reference ear for two totally different types of deafness. The former curve is for a case of oto-sclerosis (so-called "Fixation of the Stapes"), a type of middle ear deafness and the latter curve is for a case of internal ear trouble (so-called "Nerve Deafness"). The curves are alike in no respects, whatsoever. In the case of middle ear trouble there are marked depressions relative to the normal reference ear (figure 1) in the regions of 600 to 1200, 1500 to 2000, 2000 to 2500 and 3000 to 3500 cycles. There have been taken for different patients with middle ear deafness several curves and all of them agree in the location of these depressions. Some of these depressions are relative and some of them are absolute as reference to figure 4 will show. This figure (4) gives the sensitivity at the various frequencies of the ear referred to in figure 2. The two curves shown in figures 2 and 4 together give one accurate information on the physical characteristics of the defect. The stapes is not fixed but simply hindered and modified in its motion so as to produce less sensitivity than is possessed by a normal ear and also so as to give a sensitivity curve with three distinct resonant frequencies all of which are at higher frequencies than the corresponding ones for the normal reference ear and, as is to be expected, the peaks at the lower frequencies are displaced toward higher frequencies more than those in the upper part of the scale.

The curves for the case of the internal ear trouble shown in figures 3 and 5 are of much value in suggesting how the internal ear system functions physically. The patient's hearing is essentially the same as a normal ear up to about 2600 cycles as shown by figures 3 and 5; shown better in the latter, however. Then, the depression (shown better in figure 3) from 2600 to 4500 cycles is very great. When one recalls that the vibrational energy of the receiver diaphragm is proportional to the square of the receiver current, he will then grasp the significance of these curves in showing the enormous increase in the vibrational energy necessary for the patient to just hear compared with a person possessing normal hearing.

To show the ability of the person to check the data the dotted curves, taken six months later, are shown in figures 3 and 5. The curves not only check the earlier data but also show in the best possible manner that there has been no change to speak of during the six months' period. Several curves of this type have been obtained for different patients, but with the depressions showing up at different frequencies. We may ask how is it possible for so serious a defect to affect the hearing in only a single region of this sort? Without going into the anatomical evidence regarding the structure of the ear, we may say that physically the affected parts in these cases are evidently very loosely coupled (speaking mechanically) to the rest of the ear which functions normally out side of this region. Such would not be the case for middle ear trouble as shown by figures 2 and 4. The limit of audibility for this patient, who is 25 years old, is about 12000 cycles which is lower than we should expect for a person of this age. So that, the whole region above 3000 cycles (roughly speaking) is probably affected. From arguments to be presented elsewhere2 it may be that this lesion is one affecting the transverse fibres of the basilar membrane. The data at hand seem to indicate that these fibres function in somewhat the same way as postulated by Helmholtz and others (not however as pitch "determinators.") Hence, possibly the fibres above 3000 cycles are prevented from performing their proper function while those below this frequency are not yet affected.

Auditory Nerve Endings.-In concluding this brief account it is worth while to show how the data suggest the part played by the nerve endings, not as organs for changing mechanical energy into auditory nerve energy, but as organs which respond only to a very narrow range of frequencies where the pitch discrimination is good and which respond to wider ranges where the discrimination is not so good. Some curves were taken which showed that within a range of one hundred cycles the hearing decreased suddenly so that the patients were unable to hear even though the vibrational energy of the receiver diaphragm was made 10,000 times as great as was necessary for them to hear at the lower frequency and perhaps 1010 as large as was required for a normal ear to hear at the frequency in question. With this amount of energy the region of the internal ear corresponding to the lower frequency was certainly vibrating with an amplitude considerably in excess of that necessary for audibility. Yet, no tone was heard. In other words, apparently it would be necessary to stimulate the nerve corresponding to the higher frequency if the tone of the higher pitch is to be heard. So that, apparently a nerve will respond only to one frequency or a very narrow band of frequencies. The actual pitch determination, then, resides in the nerve endings which appear to have this highly selective action. It seems probable, then, that this work is leading into fields which can be explored by precise

physical measurements and fields which up to the present time have not been covered satisfactorily by other means of investigation.

The writer is greatly indebted to Dr. J. Gordon Wilson, Head of the Department of Otology Northwestern Medical School, with whom this co-operative research has been done and to whom equal credit for the success of the work is due. The writer is also indebted to Professors Millikan and Lunn of the Department of Physics of the University of Chicago for their helpful suggestions and enthusiastic interest during all the stages of development up to the present time.

1John P. Minton and J. Gordon Wilson, "Sensitivity of Normal and Defective Ears for Tones of Various Frequencies," Proc. Inst. of Medicine, Chicago, 1921.

2 John P. Minton, "Physical Characteristics of the Ear," in preparation for the Physical Review.

NON-DISJUNCTION AND THE CHROMOSOME RELATIONSHIPS OF DROSOPHILA WILLISTONI

BY REBECCA C. LANCEFIELD AND CHARLES W. METZ

STATION FOR Experimental EVOLUTION, COLD SPRING HARBOR, N. Y.

Communicated by C. B. Davenport, May 5, 1921

Of the eleven types of chromosome groups found in the genus Drosophila (Metz '16)' that designated type A is the most widespread-occurring in 13 of the 29 species that were studied. This type is represented in figure 1. It consists of one pair of rod-like chromosomes, two pairs of long, V-shaped chromosomes and (usually) one pair of very small spherical "m" chromosomes.1 The constancy of this type among the 13 species is such as to suggest a genetic homology of the respective pairs of chromosomes throughout. On the other hand the species themselves are scattered more or less at random through the genus and do not constitute a restricted taxonomic group. This suggested the desirability of a comparison of the genetic constitution of the chromosomes in two or more of these species.

Since D. melanogaster was already well known genetically and cytologically, and thus afforded a convenient basis of comparison, we undertook a study of D. willistoni, a species resembling melanogaster in appearan e and in chromosome constitution. In the course of this study we have found, by an examination of non-disjunctional flies, that the chromosomal resemblance between willistoni and melanogaster is misleading, for the sex chromosome pair of willistoni does not correspond morphologically to that of melanogaster but corresponds, rather, to one of the autosome pairs of this species. This would indicate that corresponding chromosomes in the two species are not all strictly homologous. The evidence for this conclusion together with a brief discussion is given below.