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There still remain one or two other topics introduced and commented on in this truly original work, to which we would solicit our readers' attention for a few moments, before drawing our remarks to a close and first of what M. Serres calls the Gradation of Tissues in Zoological and Embryological Formations.

"The primary or elementary tissue," says he, "in the lower Infusoria, as in the embryo during the first stage of its existence, is mere cellular substance, modified in a variety of ways. This is the common basis, so to speak, of the Monad, the Volvox, the Acephalocyst, the Ascidia, and of part of the Echinococcus and Polype. The essential properties of this tissue seem to be-1, a uniformity of function, limited to exhalation and absorption; and, 2, a power of independent existence, when a portion is detached from the rest. If to this tissue be superadded a peripheral system of blood-vessels, we advance one step in the animal scale, and come to part of the Echinodermata. If a muscular system be then added, we reach the Rotifera; and, if all these systems be combined, we arrive at the Helianthoidea. Whenever the muscular tissue is distinctly developed, we find that traces of a nervous apparatus-hitherto so blended and confused with the different parts of the animal body as not to be recognisable-begin to appear; as we observe for the first time in the Annelides, the Mollusca, and perhaps also the Crustacea. Now, a very striking analogy may be traced between these progressive gradations in zoological development and the successive changes that are discoverable in the evolving organisation of the embryo. Before impregnation, the animal is represented by a mere vesicle that consists altogether of cellular membrane enveloping an oleaginous fluid. After impregnation, the blastoderm—from which proceed the constituent parts of the embryo-exhibits two membranes; one external and serous, and the other internal and mucous. In a short time, a vascular tissue is found to be interposed between these two; and subsequently a nervous tissue makes its first appearance."

Some light has been unexpectedly thrown on this subject by the results of certain experiments, which M. Serres has recently performed on worms and leeches. "The common earth-worm," he remarks, "is very different, it is well known, in its conformation from the Polype, the Tania, the Helianthois, or the Arenicola; but, if we follow out the various metamorphoses, which the animal undergoes before it arrives at its complete development, we find that it actually does resemble each of these creatures successively according to its epoch of evolution. Now what is very remarkable is, that a counterproof of these successive advances or elevations of structure is afforded by watching the process which Nature follows in effecting the regeneration of a part, that may have been artificially destroyed. The first act of regeneration in the new-formed portion reproduces exactly the structure of an Arenicola; the second act (supposing the new-formed has been again destroyed) reproduces that of the Helianthois; while the third and last act degrades or brings the part down to the structure of a Polype.* It is obvious, therefore, that the reproductive

* M. Serres mentions that, while conducting these experiments on earthworms, he quite satisfied himself that many of the alleged different species of this and other Invertebrate animals are, in short, but the same species, only at different stages of their development. The most advanced development is the ideal type of the genus; and the least advanced constitutes the last species of it. This remark is, in an especial manner, applicable to the case of the Infusory animalcules, which have too often been most unnecessarily grouped into a great number of different families.

power becomes gradually more and more feeble, just in the same manner as we observe that the reproduction of the organic tissues in the human body become exhausted, in any part, by a frequently-repeated act of regeneration. This may be not unfrequently seen in cases of old ulcers. A first, a second, and even a third cicatrisation gives birth to a new structure that is resistant, and approaches in its characters to the normal condition of the part; but, if this act of reparation be repeated more fre. quently, the new-formed tissue becomes less and less completely organised the ulcer is then said to be atonic, and under such circumstances it often remains incurable. The same remark is applicable to tuberculous formations, which occur in the lungs and other parts of the body."

He proceeds to point out certain analogies that may be traced between the imperfect or irregular developments-in other words, the Monstrosities -that not unfrequently occur in the human embryo, and the normal structures in some of the lower animals. We must confine our notice of this curious subject to the giving of one short extract.

"These mutilations or privations of organs are incompatible with the continuance of the independent and extra-uterine life of the fœtus; but, although this be quite true, let it not be forgotten that, despite the presence of such imperfections of organisation, the creature was alive while it remained in the womb and was attached to the mother. Nay more, it may already have passed through several stages or phases of existence, and have perhaps more than completed its term of life as an Invertebrate being. Few physiologists seem to be aware that there is in these monstrous or deformed productions a scale, so to speak, of uterine viability (capability of life)-a circumstance of high philosophical importance, as it tends to shew that there is a sort of independent existence on the part of the embryo, during its intra-uterine life. Thus, a fœtus, that is destitute of an extremity only, will continue to live much longer within the womb, and thereby acquire a much higher degree of development, than another in which the heart or the brain is wanting."

In drawing these remarks to a close, we cannot but express a hope that they may excite the curiosity of some of our readers, and induce them to examine, more minutely for themselves, the highly interesting subject of Embryology in connection with that of Comparative Anatomy. No medical man can be said, in the present day, to be duly educated, if he has not acquired a tolerable knowledge of the latter science. How should it be otherwise, when we consider that Physiology can never be studied as it ought to be, without a constant reference to the organisation of all classes of animals, from the simplest Zoophyte up to Man himself? He is but the last link of the chain that extends unbroken through the long series of zoological formations, and every part of which, however dissimilar and unlike one may seem to be from another, is constructed upon a simple harmonious and kindred plan. The marvellous discoveries that have been made, of late years, in Embryology, have added not a little to the interest of this subject, and have brought to light many such unexpected analogies and features of resemblance between forms that had been hitherto imagined to be most unlike, as almost to warrant the startling observations of our author, that "Human Organogeny is only a sort of transitionary Comparative Anatomy, as in its turn Comparative Anatomy is only the fixed and permanent condition of the different phases of Hu

man Organogeny ;" and that "Animals, in a genetic point of view, may be regarded as the permanent embryos of Man.'

In contemplating the succession of phases, or stages of development, which the human being is found to exhibit during its evolution within the womb-commencing in the most simple, and terminating in the most complex form, when it reaches its mature and complete formation—are we not almost involuntarily reminded of that most interesting discovery of modern Geology, viz: that just in proportion as we trace back the history of the earth in its physical structure, by examining the older and deeper strata of its formation, so, it would seem, the more simple and uncomplicated were the forms of animal beings then in existence? In the transition rocks we meet with the fossil remains of the very lowest tribes only; in the secondary, the remains are of animals of a higher order; and it is not until we reach the more recent deposits that the bones of the mammalia are ever found. Is it not possible to trace here a sort of parallelism between the genesis of animal beings during the successive epochs of the world's formation, and that of the embryo during its successive gradations of evolutionary development? The thought is but a passing fancy: and as such only we give it. But, whether there be any truth in the conjecture or not, of this we may rest assured, that the more that we search into the hidden workings of Nature, and make ourselves acquainted with her teeming wonders, the more clearly we shall perceive a unity of design and a simplicity of operation pervading all created things, and the more strongly shall we feel that they have all been fashioned and ordained, and that they are all upheld and continued, by one Almighty hand. It has been beautifully said that

The very law which moulds a tear,
And bids it trickle from its source,
That law preserves the Earth a sphere,
And guides the planets in their course.

And so it is with the still greater marvels of the animated world. The same law, that presides over the formation of the humblest creeping thing, directs the development of him who walks the earth

"With port sublime and hopes beyond the skies."

All are alike framed on one simple and universal plan; all are created from a few, and the same simple elements; all perform similar functions; and all at length become resolved into the same component parts. Ought not the study of such a theme as that which we have been glancing at, while it exalts our admiration of the supreme wisdom and power of the Divine Architect, to serve at the same time to humiliate the pride and arrogance of Man? In his body he is but a step removed from the brutes that perish; and, at one period of his existence, he has been but as they. His structure is not more wonderful than theirs; his physical powers are in many respects inferior. It is the spirit within that alone stamps him with pre-eminence, and lifts him so far above every other earthly thing "wherein the breath of life is." Admirably hath the poet expressed the

antithetic constitution of his nature-physical as well as moral-when he exclaims

How poor, how rich how abject, how august!
How complicate, how wonderful is Man!

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WITHOUT going so far as to say he has completely made out his case, we think the author of this interesting essay has brought forward facts and opinions in reference to the functions and morbid affections of that portion of the nervous system, concerning which the most vague, unsatisfactory, and contradictory doctrines have hitherto prevailed, that must command attention and will stimulate observation by directing it into a more definite channel. That additional and multiplied researches will be required before what he has advanced can take the position of an assured fact, he does not endeavour to conceal; and, having made what must at the very least be termed a most happy suggestion, he contents himself with pointing out a few corroborations which the phenomena of disease and the action of remedies seem to supply. If more extended observation confirms the views set forth, the practical consequences will ere long exhibit themselves abundantly enough.

The contemplation of the intimate anatomical relations of the sympathetic nerve with the arterial system, induces Dr. Procter to conclude that its office consists in regulating the contractility of the blood-vessels. Nerves derived from other sources frequently accompany arteries for a long portion of their course, never, however, transmitting branches large or small to them, so that their juxta-position must be referred to some other cause than for affording facility for influencing their movements. The sympathetic, on the contrary, is emphatically the nerve of these vessels, enmeshing and penetrating them on every side, and following their minutest ramifications to their ultimate distribution. After describing the anatomical relations of the nerve Dr. Procter thus proceeds :

"The nearest approach to a positive determination of its use that we can come to with our present limited knowledge is, that it is for the purpose of regulating the tonic contraction of the arterial system, and for nothing else; however, it is difficult to expound or afford the requisite proofs of this opinion, nor am I aware that public attention has at all been called to it. I venture, therefore, allowing this idea to form the basis of my investigation, to proceed to explain my present views upon the subject, first calling the reader's attention to the remarkable fact

with which the discoveries of Sir C. Bell have made us acquainted-that there is not a part of the human body that is not supplied with two or three sets of nerves according to the simplicity or the intricacy of its functions: the excitors for sensibility, the motors for movement, and the respiratory system for the complicated purposes of respiration. When we see, by the discoveries of Dr. M. Hall, that we have a presiding and regulating power over all the sphincters and muscles of the body through the medulla oblongata and the medulla spinalis, and, in fact, that there is scarcely an organ in the human body that is not now known to have a moving and directing power; is it then probable, or even possible, that so important a system as the arterial should be without such a controlling and directing power? Acknowledging that it is not, as every one must necessarily do, and coupling this with the fact that there is a large and evidently important system of nerves exclusively surrounding, embracing, and running into the coats of the arterial system, of which we know little or nothing; and when we see the remarkable way in which anatomy bears out this opinion, I would venture to predict that so surely as anatomy led Sir C. Bell on step by step to his admirable, lucid, and conclusive arrangement of the other nervous systems, so surely does anatomy point out to us most distinctly the functions of this nervous system; and doubtless the time will arrive when it will be capable of demonstration: difficult as I confess it now appears to be, from its peculiar situation in the body, and from its apparent total want of functional connection with the other systems. It is singular that up to this period no author has sufficiently pointed out the remarkable difference in appearance and structure between the ganglia of the sympathetic and those of the spinal nerves. A single glance will be sufficient to shew this very marked difference. It is seen in the sympathetic ganglion that the nerves appear to be more like elongations of the ganglion, each coming out clear and distinct, like so many tails, the ganglion itself being of an oblong shape and smooth. In the spinal ganglia the nerves are seen entering the globe-like body of a ganglion in bundles, leaving it in the same divided or fascicular form."

After alluding to the proofs derived from the experiments of Philip, Flourens, and others, of the non-dependence of the circulation upon the cerebro-spinal system, the author, in another part of his work, thus expresses himself.

"It is self-evident, then, that it is to the sympathetic (and that alone) that we must look for regulating the arterial system. And it will be observed that in all parts of the animal body where large and sudden supplies of blood are required, such as the heart, stomach, bowels, and organs of generation, we have the ganglionic or sympathetic system very fully developed, and, as far as I can judge, in ratio to the amount of blood supplied to the several organs on the contrary, in some parts of the body, and in the extremities where the flow of blood is more regular and not subjected to those sudden calls for large supplies of blood at irregular periods, we find this nerve manifestly decreasing in size: and, indeed, as far as we can judge with the naked eye, ceasing altogether in some parts. Still I perfectly agree with Sir Charles Bell that it is distributed all over the body: but whether its influence is confined to regulating the small arteries which supply the coats of the vessels, or whether the same influence is continued by it over the whole circulating medium of the extremities and other parts that it manifestly has over the abdominal viscera, must, I fear, be left to a more enlarged enquiry."

An experiment is related which consisted in exposing the branch of the sympathetic nerve joining the ischiatic, and one of the arteries of the leg in a horse that had been killed by division of the medulla spinalis, and then connecting the nerve with the positive and the artery with the negative

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