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In examining the synovial membranes pertaining to the foot, as well as those connected with all other parts of the body, their relative importance to the sense under consideration, must not be measured by the superficial area any particular sac may present, but by the apparent amount of sensibility upon injury or in disease. Thus, for instance, from the few scanty opportunities the writer has had of observing indications of pain, during operations, etc., upon the foot, he is disposed to think that the calcaneo-cuboid and scaphoid synovial membranes, and the synovial sac dipping between the scaphoid and cuneiform bones, possess very little sensibility, if any; but that those connected with either extremity of the metatarsal bone of the great toe, possess considerably more. Indeed, many of the smaller synovial membranes placed in the phalangeal joints, and also those in the tarsal and metatarsal joints, saving those connected with the great toe, appear, from the effects of continued pressure and friction, to be worn through, or absorbed, and where such process has not been completed, their dry and almost imperceptible structure, indicates that much of their function is obliterated. Hence, after the age of 40 years, or thereabouts, and in many much earlier, the dissection and tracing of these membranes in the foot and other parts, is impossible; and, as a consequence of this destruction of structure, we shall find, as a rule, that young men and boys, from 15 to 30 years of age, possess the power of testing the value of things by weight, better than those of more advanced years. Lastly, those joints which possess the largest amount of synovial membranes, in conjunction with the greatest amount of freedom of motion in the joints which they cover, will be found endowed with the highest amount of sensibility to mechanical injury, and, also, are by far the most painful when inflamed. These latter remarks apply with much force to the synovial membrane lining the tibio-astragaloid articulation; and in experiments pertaining to the foot, the testing point in relation to the sense of force, will have especial reference to that joint, or rather, membrane. With these remarks, we may, I think, with propriety, detail a few experiments.
A poker, or pair of tongs, especially the former, is the only instrument required; also, to prevent pain from direct contact of these instruments with the skin, and to check the sensation of excess of heat or cold, it will be necessary to have the feet covered with soft and pliable leather shoes, or easy boots.
Being seated on a chair, let the foot be slightly advanced beyond the perpendicular of the knee. Let the knee and foot be everted, or turned outwards, as far as is found comfortable to the party to be experimented upon, then let the poker (or tongs) be placed between the heads of the fourth and fifth metatarsal bones ; with the poker thus adjusted, let the foot be gently raised and depressed from the heel, but rather quickly, but not so as to contract the muscles rigidly. In this position, by so moving, considerable weight will be felt. Next, revert the experiment. Retain the poker in its original position, but invert the foot, and slightly depress the external border; then elevate and depress the foot, so adjusted, as before. In this
position, very slight weight will be felt as compared with the forei going.
Again, place the foot in the position first described-everted, and apply the poker between the heads of the first and second metatarsal bones, being the site of the anterior internal axis. Next, gently raise and depress the foot as before, in this position slight weight will be felt. Revert the order of experiment. Invert the foot, depressing its external border as before described, still retaining the instrument over the internal axis, raise and depress the foot, when the feeling of weight will be found very considerable, as compared with the same weight felt with the foot everted.
What relation, it is asked, have the preceding experiments in elucidating the hypothesis here discussed ? As follows. The interior articular extremity of the tibia is divided by a slight ridge about its middle, the internal half of which is more depressed than the external, and, of course, as compared with the internal, the external half is elevated. By everting the leg and foot, the tibial articulation, in its external half, is depressed; whilst elevating the external border of the foot, and depressing the internal, the external surfaces of the tibio-astragaloid articulation are made to closely approximate each other, and the synovial membrane of the opposing surfaces, is thuswise made to approximate its own surfaces most closely. The consequences of this are, that the force, whatever it may be, passing through the joint, is uninterrupted while passing from one surface to the other; and, therefore, if direction of force has any thing to do with the sensation experienced in the joint, in such case, both synovial surfaces will be alike, so far, at least, as the line of direction is concerned. At the same time, from the nature of a shut sac, the force must be received upon one surface from behind, and on the opposite in the front; whilst, moreover, from two surfaces receiving force in the same direction, and nearly at the same instant, in the place of one surface, a larger sentient surface is exposed to the influence of its appropriate stimulus. But when the foot is inverted, and its external axis depressed, the external portion of the tibio-astragaloid articulation is widely separated from its opposing surfaces; and for a force to reach the internal portion of the articulation, in place of the external, a circuitous route must be taken, involving inuch expenditure of its original impetus, by the force having to cross the foot, and, in so doing, meet with friction sufficient to bring much of it to composition ere it reaches the principal sentient articulation, which will amply account for the diminished feeling of weight, when the foot is inverted, and a poker, or any other instrument, is resting over the external pedal axis.
When the weight is placed over the internal axis of the foot, by NEW SERIES.--NO. II. FEBRUARY 1855.
everting it, the internal articular half of the tibia, antagonizing with the opposed astragalus, is removed considerably from the adjoining surface; hence, force or vibrations, from this axis to the astragalus, have, from this unfavourable position, their intensity greatly diminished. But by inverting the foot, the opposed surfaces are brought into close approximation, and the force travelling so directly from the internal axis to the astragalus, the feeling of weight will be slightly increased to that felt in the most favourable position on the external axis, but the difference will not be perceived unless some little practice has secured accuracy.
Of course, it need scarcely be added, that in the foregoing experiments, gravitation has been used to counterpoise muscular force; and, as a natural consequence, the direction of force would be in the diagonal of either of the forces taken separately, and would reach the joint in an oblique or wave-like direction.
Let me here introduce one more experiment relating to the anterior part of the foot. In this experiment, let a poker be placed over the middle of the first metatarsal bone, when the foot is slightly inverted, and raise and depress the foot as before. In this position, the weight experienced will be greater than in any other part over which the poker may be placed on the foot; since here we have the muscular and gravitating forces antagonizing each other in a direct line with three synovial membranes; the synovial membranes covering either extremity of the first metatarsal bone, each of considerable extent in surface, and the synovial membrane of the ankle joint. The force so applied, will, of course, impress these articular surfaces better than when applied at any angle of inclination, from that of the direct line of transmissiom.
Apparent exception to the Experiments already detailed. “If a poker, tongs, or any suitable instrument, be placed upon the internal or external anterior axis of the foot (little or great toes), and the foot, with its superimposed weight, be raised upon the heel, and then be allowed to suddenly fall upon the ground in the same way as conceited minions in music attempt to beat the time for their superiors) by successively raising and depressing the foot, the consciousness of great weight will be experienced in the foot, especially about that axis upon which the instrument rests."
The feeling just described, might be supposed to arise from stronger vibratory impulses being conveyed to the several synovial membranes of the foot, especially to that lining the ankle joint; and the consciousness of increased feeling in the immediate neighbourhood, might be referred to some illusion of the sense under consideration. But the writer has no such conviction about the matter; therefore, he will here simply state, that in another paper, if spared, he shall attempt to show that the sense of force, as here maintained, has for its principal anatomical seat synovial membrane; but, from the ends its information or function are intended to secure, there are occasional departures from this general seat of distribution, the integument of the palm of the hand, the sole of the foot, and several other parts, being examples of the same.
Concerning the heel or posterior axis, it may be said that an experiment cannot be easily performed upon it, but an attempt may be made, which will elucidate the subject in a trifling degree.
Suppose, to be homely in the description, an individual, in walking across a room, has trod with his heel upon a small piece of bees’ wax, and finding it difficult to scrape it off, proceeds to balance himself on the opposite foot, whilst he flexes the leg upon the thigh of the same foot, and gently extends it for the purpose of removing the wax. Now, this last motion, or extension of the foot, is not wanted; therefore, we will suppose that the individual has troubled himself in adjusting his body, as above described, for the purpose of seeing whether or not the back of his shoe has been properly cleaned. This, then, will give the exact position here wanted." If, then, an individual, with the foot and leg thus adjusted, take a poker, and place it opposite the posterior surface of the os calcis, he will experience but slight weight at first; but after it has remained over the os calcis for some little time, the feeling of weight will greatly increase. Next, alter the position, and place the poker superiorly upon the tendo achillis, immediately opposite to the tibio-astragaloid articulation, when the feeling of weight will be felt at once, and greater than if placed above or below this situation.
The cause of this difference in the feeling of weight in the two approximate positions is obvious; when the poker rests upon the posterior inferior border of the os calcis, the greater part of its weight or force passes along the os calcis to the cuboid and metatarsal bones of the fourth and fifth toes, but part of this force not finding a ready transit from the cuboid to the metatarsal bones will be deflected, in some measure, according to its angle of incidence, towards the articular surface of the astragalus, and there occasion an increased consciousness of weight; whilst part of the weight will travel more directly (than by a course of deflection) from the calcis to the astragalus; nevertheless, whatever course force may take from the calcis when the foot is adjusted, as has been described, it is evident that before it reaches the principal sentient articulation of the foot, namely, that of the ankle-joint, much of it will have come to composition and resolution ere it has reached that point. But the reverse of all this holds good when the weight is placed exactly opposite the ankle-joint posteriorly, where both forces are brought into collision at once, and before their resultant or oblique force has been expended by friction or composition; hence, according to the present hypothesis, the greatest weight ought to be full here, and also most speedy, which exactly accords with fact.
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Here terminate what experiments I have to submit for examination on the foot. The attention will next be directed to the knee and hip-joints.
(To be continued.)
ARTICLE V.-Meissner shown to have been the first who confirmed
the fact that the Spermatozoon penetrates into the Interior of the Ovum of the Rabbit, the Animal in which such penetration was first observed. By Martin BARRY, M.D., F.R.S.
The Philosophical Magazine for May 1854 contains a note announcing that several German physiologists had at length seen the spermatozoa within the zona, not only in the ovum of the same class, but of the very animal in which I had witnessed it—the rabbit. For about a dozen years this fact of mine was by some neglected, by others ridiculed and set at nought. It seems to be viewed in a somewhat different way at the present time; for now we find an eminent physiologist making it known to whom is due the merit of giving to the said fact further confirmation. This will be seen from what follows.
On the 3d of April of the present year (1854) a declaration was published at Göttingen by R. Wagner, who says, “In the beginning (probably on the 7th or 8th) of March I had killed a female rabbit for some experiments on the heart. Dr Meissner, who was engaged in my apartment at the Physiological Institute, examined the geni tals, as the ovaries presented fresh corpora lutea. He was so fortunate as to find in the first portion of the uterus some fecundated ovum exactly like (i.e., in the same stage of development as) Figs 31 and 32 in Bischoft's work on the rabbit's ovum. Even in the first ovum, as well as then in the others, M. Meissner found spermatozoa within the zona in immediate contact with the yelk. He showed me this first ovum, and asked the presence of other persons, viz., Messrs Henle, Baum, Dr Max Müller, Theodore Weber, Dr Schrader, and several students. We all convinced ourselves of this remarkable fact hitherto denied, as is known, by Bischoff, the very man who has been most, and most deeply, occupied with the mammiferous ovum. About ten days afterwards, as appears from my correspondence list of 16th March, I wrote to Professor Leuckart of Giessen, informing him of this remarkable fact observed by Meissner on the relations of the spermatozoa to the ova. I deem it a duty to declare, that it has not been agreeable to me to hear of the publication by Professor Bischoff of what was communicated in a letter to a third person, the said publication, moreover, giving an incorrect statement of the same. Should my written communication to Professor Leuckart be generally mentioned, I must at least expect, indeed require, that mention thereof be made in a different way, and in a manner showing what my letter really said ; and that