convincing demonstration of the otolith function is that which can be obtained in the absence of all other parts which could give the same reaction. This I have been able to accomplish in the most definite way (1920b). My experiments on the otolith have been made on several species of sharks and rays. The most favorable animal for this purpose is the shovel-nosed ray or guitarfish, Rhinobatus productus. I removed all three semicircular canals with their ampullæ and then washed out the large, soft, friable otolith of the sacculus. There now remained only the small otolith of the recessus. This otolith is shaped somewhat like a plano-convex or concavo-convex lens and rests in a concave depression in which it fits much like one saucer standing in another. The concavity is lined with the characteristic macular epithelium with its hair cells. I found that if I pressed on the anterior side of this otolith the eyes rolled forward on their axes, anterior pole downward, that is, they made the same movement which occurs when the head is tilted upward. If I pressed on the hinder margin of the otolith the eyes rolled backward on their axes, the movement which occurs when the head is tilted downward. Pressure applied to the right margin of the otolith caused the right eye to be depressed and the left eye to be elevated, the same movement which results from rotating the animal to the left around its longitudinal axis, and this resulted whether the stimulus was applied to the otolith of the right or left ear. The method of stimulation just described very soon injured the delicate otolith and the movements could only be obtained a few times. When, however, I placed a small pellet of wet absorbent cotton on the otolith I could with fine forceps pull the pellet backward or forward or from side to side repeatedly without apparent injury to the otolith. When the cotton was pulled to the right the right eye went down, when pulled to the left the left eye went down, when pulled forward the eyes rolled forward on their axis, when pulled backward both eyes rolled backward.

The above experiment shows that the

a priori assignment of different functions to different otoliths with reference to the planes in which they lie and the rotational movements of the body to which they correspond does not accord with the facts. All the compensatory movements and positions arising from vestibular stimulation are obtained from this otolith alone. Parker's and my previous observation that the large otolith of the sacculus is not concerned in equilibrium is confirmed. It is of interest, too, to note that the otolith of each ear gives rise to complementary movements in both directions; elevation of the right and depression of the left eye, or depression of the right eye and elevation of the left eye can be obtained from the otolith of either ear.

III. THE MECHANISM OF THE PHYSIOLOGICAL

ACTION OF THE OTOLITH ORGANS

It has been almost universally believed since the publication of the earlier papers of Mach and Breuer that in the otolith organs the normal stimulus is the pressure due to the weight of the otolith resting on the sensitive macular epithelium; when the position of the head is changed the pressure is shifted to a different part of the macula and a different set of impulses is sent to the muscle groups concerned. This conception has been greatly strengthened by the work of Delage, Kreidl and others on the otocysts of invertebrates. But as I have shown in the preceding section stimulation experiments show with the utmost clearness and regularity results which are exactly the reverse of those which should follow if the pressure theory were true. In describing these experiments I have been repeatedly stopped to answer the question, "Don't you mean to the right' when you say to the left'?" or, "Don't you mean 'backwards' instead of 'forwards'?" When the normal animal is rotated around its longitudinal axis, to say 30° to the right, the right eye goes up and the left eye goes down. When the body is in this position the weight of the otolith in each ear must be shifted to the right. But when the right side of the otolith is pressed upon or when the cotton is

pulled to the right exactly the opposite movement of the eyes results. If as commonly believed, the stimulus is the pressure due to the weight of the otolith, and if that pressure, shifted to right by inclining the body to the right acts by stimulating more strongly the epithelium on the right hand side surely the artificial application of pressure should produce the same result but just the reverse actually happens. I believe that the actual process is as follows: When the right side of the otolith is pressed upon it is displaced to the left just as one saucer standing in another is displaced to the left when one pushes straight down on its right hand margin. This, then, is the same displacement as that which occurs when the body is tilted to the left. It is not the pressure but the displacement due to the weight of the otolith which brings about the normal stimulus. It is the direction of the displacement which determines the direction of the resulting compensatory movement. I have ventured to suggest that the displacement gives rise to differences of tension which act on the sensory structures in a manner analogous to the effects of different tensions on the vagus endings in the lungs. It will be seen in the following section that this wholly unexpected result is in accord with the conclusions which I had previously reached in regard to the mode of stimulation of the ampullæ.

IV. THE MECHANISM OF THE PHYSIOLOGICAL STIMULATION OF THE AMPULLE

An adequate discussion of the enormous literature of this subject would far exceed the limits of this paper. Nearly half a century ago Mach, Breuer and Brown almost simultaneously published papers suggesting that each canal functioned for the recognition of rotational movements in its own plane. Roughly stated the assumption was that rotation of the head in the plane of any canal would tend by the inertia of the fluid within the canal to produce a current in the direction opposite to that of the rotation. In the popular literature and in many of the text-books a favorite statement of the theory is about as

follows: Each rotation of the head in the plane of any canal causes through the inertia of the endolymph a current in the canal in a direction counter to the rotation. The hair cells of the ampullæ stick out like paddles and are deflected in the direction of the current. The bending of the hair cells exerts pressure on the nerve endings and produces the stimulus. Mach, however, was too good a physicist to believe that a current could be produced under the conditions existing in the semicircular canals. He found that water placed in a glass model of the dimensions of a human semicircular canal showed no perceptible current when rotating at a reasonable speed. He affirmed on theoretical grounds that rotation could cause a pressure but denied the possibility of an actual current. Breuer (1899) also found on anatomical grounds that the theory in this form is not tenable, for the hair cells do not project into the endolymph, but are embedded in the gelatinous mass of substance forming the cupula. In more recent years Rossi (1914) has constructed a model of the dimensions of a human canal and has been able to demonstrate some movement of the contained liquid when rotated; but the rate of rotation necessary to produce visible movement is far beyond the order of magnitude of the rate giving a distinct physiological reaction. Moreover, according to the very beautiful anatomical work of A. A. Gray (1907-08) the semicircular canals in the squirrel and the rat have each a diameter only 1/5 as great as in man. These animals show no inferiority in labyrinthine reactions. In order to form a satisfactory demonstration it would be necessary to make the external diameter of the tube in the model 0.25 mm. I have found (1912) that in the horned lizard, Phrynosoma, rotation at an angular velocity so slow as a movement through 45° in 8 seconds caused a distinct labyrinthine reflex. Under these circumstances a current is unthinkable.

Direct experiment on the canals is more to the point than the foregoing theoretical considerations. Loeb (1891) cut through or excised portions of the canals in the dogfish

and found that no disturbance of righting reactions resulted. Ewald (1892) plugged and cut the canals in the pigeon without throwing them out of function.

I have ligatured, cut and plugged the canals in the dogfish (1910) without in the least disturbing their functions. But I have put the canal current theory to a more decisive test (1919). In the dogfish the compensatory movements to rotation in the horizontal plane are mediated only by the ampullæ of the horizontal canals, and each acts only for rotation toward its own side. If one horizontal ampulla, say the left, is removed, rotation to the right around the dorsoventral axis causes both eyes to deviate to the left, but rotation to the left has no effect. I exposed a right horizontal canal for nearly its whole length, cut it through as near as possible to its posterior connection with the vestibule, then without injuring its connection with its ampulla I raised it up and fixed it in the vertical plane at right angles to the longitudinal body axis. It is evident that with the canal in this new position rotation in a horizontal plane could not cause a current in its endolymph. But rotation to the right around the dorsoventral axis actually caused both eyes to deviate to the left, while rotation to the right (or left) around the longitudinal axis, that is in the plane of the new position of the canal, did not cause such a movement. It is evident that under the conditions of the experiment rotation in a horizontal plane could not possibly produce a current in the canal, and hence the stimulation must have been produced in some other

way.

Since no further consideration need be given to the idea that the excitation on rotation is due to currents in the semicircular canals, we may briefly consider other possible causes. These might be effects due to (1) the inertia of the mass of fluid in the vestibule, or (2) due to the inertia of the ampullar contents, or (3) due to the inertia of the sensory cells themselves. The second and third of these possibilities are eliminated by the fact that when the membranous connec

tion of the utriculus has been cut off the compensatory movements to rotation in the horizontal plane are entirely absent although the motions can be as easily elicited as ever by mechanical stimulation.

Since the transection of the utriculus abolishes the reflex it is clear that the utricular (and possibly the saccular) structures are an essential part of the mechanism. It is to be noted that the direction of rotation which acts as a stimulus to any canal is that which carries foremost the side of the ampulla bearing the crista. In looking over the large number of figures given by Retzius and by A. A. Gray I find no exception to this rule. The mouths of the canals at their ampullar ends are so connected with the vestibular parts of the membraneous labyrinth that the inertia effect of the mass of liquid (endolymph and perilymph) in the vestibule must cause an increase of tension on the part of the ampulla bearing the crista when a rotation is made in the direction in which the crista leads. A careful examination of the anatomical relations will show that even if it were possible for the inertia effect of rotation to cause a movement of liquid in the canal and thus exert a pressure on the cupula (the hair cells of course could not be acted upon directly), a much greater effect must be produced on the membranous structures in the vestibule. The relatively large mass of liquid in the vestibule with its proportionally small surface area exposed to the friction of the walls must show more inertia effect during rotation than the small amount of liquid in the canal with its proportionally large area of contact with the canal walls. The membranes which form the sacculus and utriculus are virtually stretched through the mass of liquid in the vestibule and must necessarily be put under tension when any rotational movement is given to the liquid.

If the above conception is the correct one it should be true that change of tension and not change of pressure should act as the stimulus. I had previously shown by experiments on Phrynosoma (1912) that the pressure due to centrifugal force has nothing to

do with the excitation. When the animal was placed with its head 25 mm. from the center of rotation it required no greater rate of rotation to act as a stimulus than when the head was 300 mm. from the center. The centrifugal force in the latter position is 12 times as great as in the former, but the angular velocity and hence the torsion effect was the same in the two positions.

Convection currents due to a difference in temperature on the two sides of the vestibule could much more conceivably occur in the liquid of the vestibule than in the canals. The nystagmus movements described by Högyes as a result of irrigating the external ear of man and many animals with hot or cold water and the change of character of the nystagmus by change of position of the head can best be accounted for by the changes of density of the liquid in the vestibule. The reliability of Bárány's use of these phenomena for diagnostic purposes is not affected by the acceptance of this view, but only his unscientific explanation must be abandoned.

I wish in closing to draw attention to the fact that a survey of all the experimental work on the labyrinth leads to the conclusion that the stimulation of the vestibular structures and of the sensory endings in the ampullæ depend upon the same principle, namely the effects of changes of relative tensions. How the change of tension excites the nerve endings and what part if any the hair cells play in the process still remains wholly outside the field of experimental investigation.

Lee, Frederic S.

1893. A study of the sense of equilibrium in fishes. Journal of Physiol., 15: 311.

Loeb, J. 1891. Ueber Geotropismus bei Thieren. Arch. f. d. ges. Physiol., 49: 175.

Maxwell, S. S.

1910. Experiments on the functions of the internal ear. Univ. of Calif. Pub. in Physiol., 4: 1.

1912.

On the exciting cause of compensatory movements. Am. Jour. of Physiol., 29: 367.

1919. Labyrinth and Equilibrium. I. A comparison of the effect of removal of the otolith organs and of the semicircular canals. Jour. of Gen. Physiol., 2: 123. 1920a. Labyrinth and Equilibrium. II. The mechanism of the dynamic functions of the labyrinth. Jour. of Gen. Physiol., 2: 349.

19206. Labyrinth and Equilibrium. III. The mechanism of the static functions of the labyrinth. Jour, of Gen. Physiol., 3: 157.

Parker, G. H.

1909. Influence of the eyes, ears and other allied sense organs on the movements of the dogfish, Mustelus Canis (Mitchill). Bull, Bureau of Fisheries, 29: 43.

Rossi, G. 1914. Di un modello per studiare gli spostamenti della endolinfa nei canali semicircolari. Arch. di Fisiol., 12: 349.

MEETING OF THE GENETICISTS
INTERESTED IN AGRICULTURE

IN conjunction with the meetings of the American Association for the Advancement of Science and affiliated societies in Chicago an informal gathering of instructors and investigators of genetics related to agriculture was held December 28th at the University of Chicago. Some thirty-five representatives from fifteen Agricultural Colleges and Experiment Stations, the United States Department of Agriculture and other institutions were present. Unfortunately the impossibility of getting the final notices out until very late prevented a number of others from attending. The purpose of the meeting was to discuss such topics of mutual interest at this time as

departmental organization, the place of genetics in the curriculum in agricultural colleges and cooperation in genetic investigations.

In order to open up the subject and start the discussion the above topics were assigned in advance by Professor L. J. Cole, of Wisconsin, who was largely instrumental in bringing about the meeting. In the carrying out of this plan Professors J. A. Detlefsen, Illinois, and R. A. Emerson, Cornell, spoke on organization. In their talks and the discussion which followed it was shown that in many institutions the instruction and research in genetics are scattered about in many different departments with no one person or department responsible for a fundamental course in genetics. In other institutions some genetics is taught in all departments with the emphasis laid in some one department, while in other institutions a separate department of genetics has been established which assumes all responsibility for genetics although other departments may give some special courses and carry on particular lines of research where the staff is interested and well fitted to do such work. All were agreed that a fundamental, general course of genetics should be required before taking up any applied courses in breeding, but in what department that course should be given is a secondary matter to be determined by existing conditions. Many thought it to be desirable for the teaching staff to keep in touch with applied problems of genetics by carrying on investigations of a practical nature although it would be unwise to limit either the theoretical or applied research to a single department of genetics as the outcome of such experiments depends so largely on familiarity with the material worked with and individual interest in particular problems.

In order to bring the general conclusions to the attention of the authorities of the agricultural colleges and experiment stations a committee was appointed to draw up a statement which would embody in a general way the consensus of opinion of this meeting in regard to the matter of departmental organi

zations. The following resolution was prepared and adopted:

As far as consistent with present organization in agricultural colleges a single department of genetics, prepared to handle the elementary and advanced courses of general genetics and to direct the investigational work on the basic principles of genetics, has certain practical advantages in that such an arrangement: (1) simplifies administration and prevents unnecessary duplication; (2) identifies and gives standing to the subject of genetics in the curriculum; and (3) unifies instruction and research. Such a department should not attempt to control all the investigational work in specialized subjects on either the applied or theoretical problems of genetics but would be able to cooperate in every way possible to advance the outcome of such investigations.

The place of genetics in the agricultural curriculum was discussed by Professors E. B. Babcock, California, and S. A. Beach, Iowa. In their presentations and in the discussion which followed it was stated that it is theoretically desirable that a general course in genetics should be required of all students of agriculture but that in practise it is not always possible to do this. Most institutions require genetics of students taking certain courses, particularly those concerned directly with plant and animal production. In other institutions genetics is optional with the stuIdent or left to the student advisers. Laboratory work is not always required except of those students who intend to specialize in genetics. A general course in genetics should come as early in the curriculum as possible, usually in the second or third year, and should follow an elementary course in biology or its equivalent and precede any of the courses in applied genetics. This would seem to be self-evident but as now practised this is not always the case. There should, furthermore, be only one such elementary course, in whatever department given, which should treat of the general principles and lay the foundation for further application to special subjects.

The subject of cooperation in genetic investigation was discussed by Professor M. J.