take place around the base of the original one, and develop in the same way. The formation of the echinococcus from the mass of cells seems to take place by their coalescence, and retiring from the centre so as to leave a tubular canal, which Mr. Wilson believes to be modified, so as to form in the body the retractor muscle of the head, and exterior to it the peduncle.

A ciliary movement has been seen by M. Lebert in the interior of echinococci; it does not, however, appear to be a constant phenomenon. We have never seen it ourselves. Among the multitudes of living echinococci, some are found which are shrivelled, altered in shape, more opaque than the others, and filled with an opaque granular mass. These are doubtless dead, and, at the same time, traces of others, which have completely decayed, are discernible in the shape of detached hooklets. When, as occasionally happens, a cyst, such as we have above described, is entirely barren of echinococci, it is properly termed an acephalocyst. This is much more frequently, we think, the case with the secondary and tertiary than with the primary cyst. We cannot hesitate for a moment to regard the cyst productions as simply results of a peculiar exudative process, and not as in the least partaking of the character of animals. The exterior envelop is derived from the natural tissues of the affected part; the interior, which can alone be considered as proper to the acephalocyst, can scarcely be said to be organized, not, we think, certainly so much as the successive layers of false membrane, which are formed upon an inflamed serous surface. Neither can we consider the acephalocyst as a "gigantic organic cell," as all we know of its origin is entirely opposed to such an idea. Its relation to the echinococci is, in all probability, that of affording a suitable nidus for their formation and development; but it is by no means clear why, in some acephalocysts, the animal cells are wanting; or why, in others inhabited by them, no secondary cysts are produced. Perhaps it may be found that the development of echinococci and secondary cysts takes place in an inverse ratio to each other. The cysts, both primary and secondary, are subject to degenerate; they become less tensely filled, their walls softer and more gelatinous, their contents turbid with diffused granulous matter and debris of echinococci. At last they shrivel up into a caseous mass, which is often the seat of calcareous deposit. A variable number of its progeny may decay in this manner, without the parent cyst itself being similarly affected. Inflammation of the external enveloping cyst is the chief cause of the destruction of the primary formation in contact with it; this is sometimes very acute, and leads to the formation of an abscess, which subsequently opens externally, or into some of the adjacent cavities or canals. The debris of the acephalocyst and its contents may be evacuated in this way, and as the cavity contracts and closes a cure is effected. When the inflammation is more chronic, the exudation which is poured out into the cavity of the primary cyst seems to derange the nutrition of the included ones, so that they shrink up and degenerate into mere laminæ, of cheesy consistence; these, together with an oily calcareous residue of the fluid contents, which are gradually absorbed, remain in the interior of the primary cyst, which itself wastes and shrinks like its included progeny. In this way, another kind of cure of

the disease takes place, as the degenerated mass may remain for an indefinite time in the substance of a part, without giving rise to any symptoms. Such degenerated acephalocysts have, it would appear, been mistaken for tubercle. The following organs are occasionally the seat of acephalocysts. The liver, xar' ozny, the peritoneum, and the underlying areolar tissue, the muscles, the brain, the spleen, the kidneys, the lungs, the bones. They not uncommonly occur in several parts at the same time. The only injurious effects ordinarily caused by acephalocysts, are such as result from pressure on important parts. It may, perhaps, happen that they cause exhaustion when very numerous. It may be well to add a caution, with respect to Pseudo-parasites, as they are termed. These are either real animals, which are mingled with the excretions by impostors, or substances which are really produced in the body, but are not animals at all. It may sometimes require a more than ordinary acquaintance with parasitic animals to arrive at the truth.

THE PATHOLOGICAL ANATOMY OF THE

NERVOUS SYSTEM.

CHAPTER VI.

GENERAL OBSERVATIONS.

In no organ or system of the human body is there such an apparent want of accordance and definite relation between the symptoms of disease and the structural derangements and changes produced by it, as in the nervous system at large. This is due to various causes. In the first place, our physiological knowledge of the laws governing the action. of the nervous system is not on a par with our acquaintance with the processes operating in other organs; chemistry, physics, mechanics, can be called to aid in the investigation of the healthy and diseased states of the bones, the soft tissues investing them, the thoracic or abdominal viscera; and the structure of these parts is more analogous to what meets the eye of the scientific observer in other departments of nature. The only agent to which nervous functions can be compared, eludes our senses, except in its manifestations, as much as the operations of the cerebro-spinal energies themselves; we can judge of galvanism and electricity by the effects they produce, but we do not see their modus operandi; and we have not even succeeded in demonstrating, as yet, the existence, in the brain or spinal cord, of a structure which may legitimately be concluded to generate a force, in a manner similar to the production of that powerful agent, which is now metamorphosing the human race. It is, then, manifestly impossible, if we are imperfectly acquainted with the laws governing the nervous system in health, that we should be able, sufficiently, to define and appreciate the deviations from the healthy standard; and, in many instances, we must be satisfied to refer for explanation of the symptoms we meet with, to hypothetical analogies, or confess our entire incapability of accounting for the phenomena before us. A correct appreciation of the symptoms of disease is a point which next may be fairly demanded of us, if we attempt to explain or seek for morbid phenomena after death; thanks to Sir Charles Bell, Flourens, Marshall Hall, Romberg, and other distinguished inquirers of the present age, much has been cleared up, which previously appeared an impenetrable mystery; but our means of physical diagnosis are still but scanty; we are left, in a large num

ber of cases, to form our opinions from the subjective statements of the patient; and where these fail us, as in early childhood, or in certain forms of disease, the greatest empirical experience may be inadequate to offer an explanation of the symptoms, or even to determine their exact relation to ccrebral lesions. The peculiar connection of the brain with our mental powers and the soul, will, necessarily, ever place it in a different position, in regard to physical research, than other organs of the body, and in no department of natural science is the caution more necessary, that we should not mistake that which is unattainable to science, and that which the Creator has allowed to be within our reach; and, valuable as are vivisections, and other experiments, made upon the lower animals, in reference to neurology, we must never forget, on the one hand, the disturbance to the ordinary laws of action. likely to be produced by the injuries themselves; and on the other, the chasm which intervenes between the brute creation and the human species. We cannot allude to the subject of the diagnosis of nervous disease, without dwelling, forcibly, on the necessity for availing ourselves of those means which, limited as they may be, are yet not used as uniformly and perseveringly as they are applied for the investigation of other morbid states of the body. A close examination by the eye and by the hand should be made of the cranium, the spinal column, and the courses of affected nerves; the thermometer and the dynamometer should be brought into more frequent use, and more accurate tests of the sensibility and mobility, and other functions of the nervous system, ought to be employed than have hitherto generally prevailed.

The researches of Bright, Frerichs, and others, have demonstrated the close relation of the state of the blood to cerebral disease; and science has shown, what, previously, was purely hypothetical, that the most fatal conditions may be thus induced without any palpable changes being wrought in the cerebral tissues. It does not, however, follow that, because we see no changes, none have taken place. The poison that we know to be in the blood may elude our chemical tests, and yet cause death. Then, seeing how limited our knowledge of the nervous system is, it is not to be wondered at that, although the manifestation of altered function is so great as to force the belief in its altered constitution, it is not in our power to prove the latter to the perception; but, as Dr. Watson remarks, "whatever may be the nature of the unknown, and, perhaps, fugitive physical conditions of the nervous centres, thus capable of disturbing, or abolishing their functions, it is useful to keep in our minds a distinct and clear conception of the fact, that there must be some such physical conditions."

In examining the pathology of the nervous system, we shall adopt the succession usually followed by medical writers, and consider, first, the brain and its membranes; next, the spinal cord, with its membranes; third, the cerebro-spinal nerves, and the subject will be concluded by a summary of what is known with regard to the sympathetic.

CHAPTER VII.

THE DURA MATER.

THE intimate relation existing between the dura mater and the cranium renders it peculiarly prone to sympathetic affections propagated from the bone, and from its proximity to the latter it is most likely to be involved in injuries of a traumatic nature. As on its external surface the close contact with the cranium favors a communication of disease from without, so the relation of its internal surface to the arachnoid induces a liability to communication of morbid action from within. The amount of idiopathic disease discoverable in the dura mater in the deadhouse is not great; though we are justified, by its character as a fibroserous membrane, in assuming that it is frequently affected during life; thus, the headaches complained of by patients affected with chronic rheumatism may often fairly be set down to a diseased condition of the dura mater, both from the resemblance which its symptoms offer to those occurring in rheumatism of other fibro-serous membranes, and from the success resulting from an anti-rheumatic treatment. It is not the general character of rheumatism to cause marked or extensive disorganization when attacking membranous expansions, and there are no especial reasons to expect a deviation from this rule in regard to the fibrous covering of the brain. A considerable difference exists in the adhesion between the dura mater and the cranium at different periods of life, independently of disease; the connection is lax in childhood, and is rendered more intimate and firm with advancing age, as the sutures become ossified and the bones lose their resiliency. It is especially in the latter period that external injuries are liable to implicate the dura mater as well as the bone, and one of the most common effects of blows or concussions is a forcible separation of the membrane, with hemorrhage between it and the bone. The clot may, as elsewhere, be partially or entirely absorbed, and we accordingly meet with it in the various stages of metamorphosis. One form of hemorrhage in this region is connate, and is termed cephalhæmatoma;' it is produced by the pressure exerted during parturition, and is generally found in the form of a tumor, varying in size from a walnut to a child's head, on the parietal bone, presenting during labor. As this, however, is rather an affection of the pericranium, we shall revert to it when speaking of the morbid anatomy of the bones. We may state that nature adopts the same process of limitation and absorption in the case of the external as in the internal hemorrhage.

Deriv. xpaλn, head; and alμáropa, sanguineous tumor.