5. That the special action of vanadium on the function of respiration is to cause (a) A stimulation, followed by (b) A depression of respiration, the latter being not continuous, but intermittent. Both effects are considered to be due to an action of the poison upon the respiratory nervous centre. 6. That the special action of vanadium on the function of circulation is to cause (a) A diminution of blood-pressure, which is not continuous, but intermits during the operation of the poison; (b) A disappearance of respiration-curves; (c) A diminution and irregularity of pulse, which is also intermittent. The results are considered to be due to an action of the poison on the vaso-motor centre and on the intracardiac nervous mechanism. 7. That, although muscles and nerve-trunks speedily die when immersed in even dilute solutions of a sodium salt of vanadium, yet vanadium is not rightly to be called a muscle- and nerve-poison, since frogs which have been poisoned by subcutaneous injection of vanadium still possess nerves and muscles which, in irritability or in power of doing work, are quite normal. Nevertheless vanadium attacks the nervous centres of the spinal cord and medulla oblongata. Observations on the Physiological Action of Chromium. By JOHN PRIESTLEY. The author experimented with guinea-pigs, rabbits, and frogs, injecting solutions of neutral chromate of sodium (Na,CrO) beneath the skin or into the veins. He concludes: 1. That 1 to 3 grm. CrO,, in the form of the above-named salt, is a powerful poison for rabbits and guinea-pigs. 2. That death is preceded by spasms and violent retching, which commence a few minutes after injection of the poison. Spasms are succeeded by paralysis of motion and, in frogs, abolition of reflex action. 3. That the blood-pressure first rises and then falls, the fall continuing until death. Further, that after the fall has become marked the pulse suddenly becomes abnormal, stopping for the space of a beat or two at irregular intervals, which are occasionally of considerable length, the pulse becoming regular again during the intervals. The author believes that this irregularity of pulse is due to an action on the vagus nervous centre. 4. That the alimentary mucous membranes are the seat of extensive congestion and ecchymoses. 5. That the kidneys become congested. 6. That muscles and nerve-trunks and extremities remain sensibly normal. The Termination of the Nerves in the Vestibule and Semicircular Canals of Mammals. By URBAN PRITCHARD, M.D., F.R.C.S., Aural Surgeon to King's College Hospital, Lecturer on Animal Physiology at King's College. The author gave the results of his investigations into the structure of the nerve epithelium, as it is called, which contains the terminal distribution of the acoustic nerve. The membranous labyrinth is composed of three layers-externally some loose connective tissue, then a distinct layer of dense connective tissue (the tunica propria), and lying on this a single layer of tessellated epithelium. At the acoustic spots, where the nerve is distributed, this membrane is firmly adherent to the Osseous wall, and the epithelial layer becomes transformed into nerve epithelium. In the saccule and utricle these spots are termed the maculæ acusticæ, and in the three ampull the crista acustica, the latter being raised into a kind of ridge. The nerve epithelium.-Max Schultze described this structure as consisting of three elements-a deep layer of nuclei, a superficial layer of cylindrical cells, and between them numerous filiform cells. Odenius and Kölliker's researches confirmed these observations, but Hasse gives a totally different account of the structure. He describes it as consisting of alternating elongated cells, the one bearing the cilium, the other isolating the ciliated cells, and resting with a broad base on the membrana propria. Rudinger somewhat reverses the description of Hasse, and states that the isolating cells are triangular, with their bases turned upwards so as to form the free border of the epithelial mass, and doubts the existence of the deep layer of nuclei. Ebner believes the essential elements to consist of two forms-a superficial layer of cylindrical ciliated cells rounded off below, and a deep multiple layer of filiform cells with their filaments passing up between the cylindrical cells. Lastly, Paul Meyer describes it as made of two parts-a deep layer of nuclei, and a superficial one of cylindrical ciliated cells tapering off below. The author's observations have led him to conclusions which, although they are essentially different from those of the authors just alluded to, yet appear to him to reconcile to a great degree their various conflicting descriptions. The appearance of this structure differs according to the position in the macula of the portion examined. A typical portion, such as may be seen midway between the centre and circumference of the spot, consists of a layer of alternating elongated cells, bordered above by a distinct cuticular membrane, and connected below with those nuclei which form the deep layer described by most authors. So that the cellular clements may be said to consist of two alternating forms of elongated cells, each having an upper and a lower nucleus. The author calls the first the thorn-cells, on account of the shape of their cilium, and the second the bristle-cells for a similar reason. The thorn-cells have a fusiform body containing an oval nucleus; from this body passes upwards through the cuticular membrane a tapering cilium or thorn; the fower extremity is prolonged downwards, and again expands to enclose its second nucleus. The bristle-cells have a triangular body containing an oval nucleus; the base of this is intimately connected with the cuticular membrane, and from this base passes upwards a narrow bristle-like cilium; the apex of this triangular body is prolonged downwards and has a second nucleus like its fellow thorn-cell. The cuticular membrane is a very thick, well-marked membrane, holding the cellular elements in their place, and perforated for the passage of the cilia. This membrane is analogous to the membrana reticularis of the organ of Corti, and the author therefore proposes to call it by the same name. Modifications of the nerve epithelium.-As there is a general increase in thickness of the macula from circumference to centre, so the cells and their various parts elongate; the cilia, which are short and stumpy at the edge, become very much longer and comparatively finer at the centre of the acoustic spot. At the circumference the cells pass by insensible gradations into the columnar epithelial cells, which surround the whole macula. Towards the centre the upper nucleus and surrounding protoplasm of the bristle-cells gradually diminish and then are lost altogether, this part of the cell being represented by a trabecula from the membrana reticularis. The bristle-like cilium remains after the upper protoplasmic mass has disappeared; but eventually this also is lost. The termination of the nerves in the macula.-The nerve-fibres arriving at the membrana propria lose their white substance, and enter the nerve epithelium without it. After passing this point there is considerable difficulty in tracing the nerve-filaments; but there is no doubt that they form a plexus around the deeper layer of nuclear bodies, and that some of the filaments may be traced directly or indirectly into the ciliated cells. The otolith mass.-Covering the acoustic spot is a soft mass into which the cilia project to a certain distance; this is evidently of a cuticular nature, and is analogous to the membrana tectoria of the cochlea. The otoliths are fixed by this mass, being chiefly contained in its outer portion. 1876. 15 On a Microscope adapted for showing the Circulation in the IIuman Subject. By Dr. URBAN PRITCHARD. Physiology of the Nervous System of Meduse. Fundamental Observations.—The author has succeeded in demonstrating the presence of a nervous system in Meduse, the ganglionic element of which appears to be localized exclusively in the margin of the swimming-bell. For he found that on excising the entire margin of the bell in any species of naked-eyed Medusa the swimming motions of the bell instantly ceased and were never again resumed, while the severed margin continued its rhythmical contractions for days. With the covered-eyed Medusa the case is not quite so definite; for although the paralysis of the bell, which is here likewise produced by the operation just described, is usually complete for a time, it is not always permanent; but, after periods varying from a few seconds to half an hour or more, occasional contractions begin to manifest themselves. Moreover, in the case of the covered-eyed Medusa, the author found that excision of the lithocysts alone was attended with the same degree of paralyzing effect on the bell as was excision of the entire margin; whereas in the case of the naked-eyed Meduse such was not the case. Histological observations revealed the presence of ganglion-cells and nerve-fibres in the lithocysts. Natural Rhythm-As regards the natural rhythm of the Meduse, it was observed that its rate has a tendency to bear an inverse proportion to the size of the individual; but that on submitting an individual to artificial segmentation, the rate of the rhythm exhibited by the various segments showed a tendency, other things equal, to vary directly as the size of the segment. When forms of mutilation were practised in which the margin of the swimmingbell was left intact, it was observed that after a temporary acceleration the rate of the rhythm progressively declined, and became stationary at a rate that was slower the greater the amount of tissue that had been removed. From these experiments the author is inclined to infer that the apparently automatic action on the part of the marginal ganglia is really of the nature of a reflex-a constant stimulation being presumably supplied by those other parts of the organism the removal of which was attended with a retardation of the rhythm. The rate of the rhythm is increased by elevations of temperature as far as 60° F., but in still warmer water (70°-80°) the rate, after having been temporarily quickened, becomes permanently slowed. Diminution of temperature likewise produces a retarding effect on the rhythm, and eventually (20°) altogether stops it. Some specimens of Aurelia aurita were frozen solid, so that all their gelatinous tissues were pierced through in every direction by an innumerable multitude of ice crystals, which had been formed by the freezing, in situ, of the sea-water which enters so largely into the composition of these tissues. Yet, on being thawed out, the animals recovered, although their original rate of rhythm did not fully return. Their tissues then presented a ragged appearance, which was due to the disintegrating effect produced by the formation of the ice crystals. The rate of the rhythm is accelerated by oxygen and retarded by carbonic acid. Stimulation.-All the contractile tissues of all the Medusæ are keenly sensitive to all kinds of stimulation. When a swimming-bell, for instance, is paralyzed by excision of its margin, it invariably responds to a single stimulus by once performing that movement which it would have performed in response to that stimulus had it still been in an unmutilated state. To mechanical stimulation the sensitiveness of the paralyzed bells is wonderfully great-a drop of sea-water let fall from an inch in height upon the contractile tissue being sufficient, in some species, to elicit a responsive contraction. In their responses to all kinds of chemical stimuli, the excitable tissues of the Meduse conform in every respect to the rules which are followed by the nervo-muscular tissues of higher animals. Similarly with thermal and electrical stimulation. Light also acts as a powerful and unfailing stimulus in the cases of some of the naked-eyed Medusse. Sarsia, for instance, almost invariably responds to a single flash by giving one or more contractions. On removing the margin such responses cease on the part of the bell, although they continue on the part of the severed margin. But on removing the so-called "eyespecks" from the margin such responses cease; and that these "eye-specks" are true visual organs is further proved by the fact that, while unmutilated Sarsia will throng into the path of a beam of light, and even follow the beam wherever it is moved through the water, Sarsia with their "eye-specks" removed will no longer do so. Any one of the luminous rays of the spectrum acts as a stimulus, but not so the rays which lie on either side of the luminous spectrum. The period of latent stimulation was determined in the case of Aurelia aurita by employing the induction-shock. It was found to vary greatly, according to the temperature at which the tissue was kept. Thus, while in water at 20° it was sec., in water at 70° it was sec. It was also found to vary greatly under the influence of so-called summation of stimuli. Thus, while in water at 45° the latent period was sec. in the case of the first of a series of stimuli supplied in regular succession at two seconds' interval, it was only sec. in the case of the tenth stimulus of the series. In every such series of stimuli supplied at short intervals the latent period becomes progressively less and less until it attains its minimum, while the strength of the contraction becomes progressively greater and greater until it attains its maximum, the intensity of the stimulation, of course, remaining constant throughout the series. If more than one minute is allowed to elapse between any two successive stimuli of a series, this beneficial or arousing effect of summation no longer asserts itself; the tissue has, as it were, forgotten the occurrence of the previous stimuli. That the arousing effect in question is due to the occurrence of the successive stimulations, and not to the occurrence of the successive contractions, appears to be indicated by the fact that if induction-shocks be employed which are of less than minimal intensity at the commencement of a series, they first become of minimal and eventually, at the end of a series, of more than minimal intensity. Now, as in this case no contraction occurs in response to the first three or four stimuli, it is evident that the summating influence must have reference to the process of stimulation as distinguished from that of contraction. Nevertheless, that the summating effect is a general one pervading the whole extent of the responding tissue, and not confined to the area occupied by the electrodes, is proved by the fact that if, during the administration of a series of stimuli, the electrodes be suddenly shifted to another part of the excitable tissue (perhaps eight or nine inches from their previous seat), the summating effect is resumed from the point at which it was left by the previous stimulus. The author further proved by various experiments that during the natural swimming motions of the Medusæ every contraction exerts a beneficial influence on its successor, which resembles both in kind and degree that which is exerted by a contraction due to an artificial stimulus. Artificial Rhythm.-When the paralyzed disk of Aurelia aurita is submitted to strong faradaic stimulation, it goes into a tolerably well-pronounced tetanus. If the strength of the current be now diminished, the tetanus assumes a wild and tumultuous charac➡ ter, somewhat resembling that of a heart under similar circumstances. If the strength of the current be again progressively diminished the character of the tetanus becomes progressively less and less tumultuous, until at last it ceases to be tetanus and passes into rhythm. This artificial rhythm is quite as regular and quite as sustained as is the natural rhythm of the animal. Its rate varies in different specimens, but usually corresponds with that of rapid swimming. Progressively diminishing the strength of the faradaic stimulation has the effect of progressively decreasing the rate of the rhythm down to the point at which all response ceases; but between the slowest rhythm obtainable by minimal stimulation and the most rapid rhythm obtainable before the appearance of tetanus there are numerous degrees of rate to be observed. The artificial rhythm may be obtained with a portion of any size of irritable tissue, and whether a small or a large piece of the latter be included between the electrodes. The persistency of any given rate of rhythm under the same strength of current is wonderfully great; for it generally requires more than an hour of continuous faradization before the rhythm begins to become irregular, owing to incipient exhaustion. At first only one systole is omitted at long intervals, but afterwards these omissions become frequent and all the contractions irregular. Finally the contractions altogether cease, but a rest of half an hour or an hour restores the irritability. The hypothesis by which the author seeks to explain this artificial rhythm (a rhythm which, in most cases, is quite as regular as the beating of a heart) is as follows:- Every time the tissue contracts it must, as a consequence, suffer a certain degree of exhaustion, and therefore must become slightly less sensitive to stimulation than it was before. After a time, however, the exhaustion will pass away, and the original degree of sensitiveness will thereupon return. Now the intensity of the faradaic stimulation, which is alone capable of producing rhythmic response, is either minimal, or but slightly more than minimal, in relation to the sensitiveness of the tissue when fresh. Consequently, when the degree of this sensitiveness is somewhat lowered by temporary exhaustion, the intensity of the stimulation becomes somewhat less than minimal in relation to this lower degree of sensitiveness. The tissue therefore fails to perceive the presence of the stimulus, and consequently fails to respond. But so soon as the exhaustion is completely recovered from, so soon will the tissue again perceive the presence of the stimulation. It will therefore again respond, again become temporarily exhausted, again fail to perceive the presence of the stimulation, and therefore again become temporarily quiescent. Now it is obvious that if this process occurs once, it may occur an indefinite number of times; and as the conditions of nutrition, as well as those of stimulation, remain constant, it is manifest that the responses may thus become periodic. In order to test this hypothesis the author made the following experiments. Having first noted the rate of the rhythm under faradaic stimulation of minimal intensity, without shifting the electrodes or altering the strength of the current, he discarded the faradaic stimulation, and substituted for it single induction-shocks thrown in with a key. He found that the maximum number of these single shocks which he could thus throw in in a given time, so as to procure a response to every shock, corresponded exactly with the number of contractions which the tissue had previously given during a similar interval of time when under the influence of the faradaic current of similar intensity. For instance, to take a specific case, it was found that under the faradaic current the rate of the rhythm was one in two seconds. By now throwing in single shocks of the same intensity, it was found that the quickest rate at which these could be thrown in, so as to procure a response to every shock, was one in two seconds. If thrown in at a slightly quicker rate, every now and then, at regular intervals, one of the shocks would fail to elicit a response. The length of these intervals, of course, depended on the rate at which the successive shocks were thrown in; so that, for instance, if they were thrown in at the rate of one a second, the tissue would only, but always, respond to every alternate shock. As The following, and somewhat similar, experiment is still more conclusive. already stated, the rate of the artificial rhythm under faradaic stimulation varies with the strength of the faradaic current. Now, by choosing at random any strength of faradaic stimulation between the limits where rhythmic response occurred, and by noting the rate of the rhythm under that strength, the author was generally able to predict the precise number of single induction-shocks he could afterwards afford to throw in with the same strength of current, so as to procure a response to every shock-this number, of course, corresponding exactly with the rate of the rhythm previously manifested under the faradaic stimulation. Other experiments, which do not admit of being briefly detailed, have likewise confirmed the above hypothesis. Upon this hypothesis, therefore, the author has constructed a theory concerning the rhythmic action of organic tissues in general. The details of this theory cannot be rendered in the present abstract; but in its main outlines it is very simple, viz. that all such rhythmic action is due to the alternate process of exhaustion and recovery of contractile tissues, which has just been explained. Therefore the particular case of rhythmic action of ganglionated tissues is supposed by this theory to be due, not to any special resistance mechanism on the part of the ganglionic tissues, but to the primary qualities of the contractile tissues. In other words, the function of the ganglia is supposed to be merely that of |