Part 20

These two things, the great development of the nervous system and the frequency of its action in the infant, make the diseases of this system the predominant ones at that age. So great is the susceptibility of the brain in answering to sympathetic excitements, that if pains are at all severe in any part, they immediately produce convulsions, which are at least four times more frequent at this age than any of the following. I would observe upon this subject, that the different systems are more or less disposed in the different ages, to answer to sympathies, according as their predominance in the economy is more or less decided. The same morbific cause, fixed upon any organ, which produces convulsions in an infant by acting sympathetically upon the brain, would give to a young girl a suppression of the catamenia, by influencing the womb, which then begins to predominate; to a strong vigorous young man, a peripneumony; to an adult, in whom the gastric viscera predominate, an affection of these viscera, &c. It is thus that the same passions that would give to this one a jaundice, engorgement of the liver, &c. would produce more particularly in an infant an epilepsy, which attacks the brain.

The nervous functions are not only frequently deranged by sympathy in infancy, but it is particularly at this age that the greatest number of organic diseases is found in the brain, the spinal marrow, the nerves, or the organs that depend upon them. Cerebral fungi, hydrocephalus, spina bifida, &c. are a proof of this. The great quantity of blood that goes at that period to the nervous system has much influence upon this phenomenon; now this quantity is brought there by the predominance of the vital forces.

In proportion as the infant grows, its nervous system and the brain, which is the centre of it, lose by degrees the predominance that characterize them. Their diseases become less frequent. They are brought finally to the level of the other systems.

III. _State of the nervous system after growth._

At puberty, the empire of the brain, which is insensibly diminished, gives place to that of the genital organs, which have a sudden increase. The cerebral nerves appear to me to have but little influence upon their development, as well as upon that of most of the other systems. Observe, in fact, that all the phenomena of generation are governed by the organic forces, which, as we have seen, are absolutely independent of the nerves. Thus the great excitement of the genital organs, from which arise satyriasis, nymphomania, &c. have no analogy with convulsions whose principle is in the brain; as the destruction of the venereal appetite is wholly disconnected with the phenomena of palsies. This is so true, that often during those that affect the lower half of the body by a fall on the sacrum, or by any other cause, the secretion of semen and venereal desires take place as usual.

Beyond puberty, and towards the adult age, when the general equilibrium is more nearly established among the different systems, the nervous is not affected more than those of which we have had occasion to speak in treating of this system.

IV. _State of the nervous system in old age._

At this period of life, the nervous cerebral system has but very few functions to perform. As to sensation, this being almost blunted by habit, is the reason why external bodies make but little impression upon the organs of sense; many of these, especially the eye and the ear, are often shut to sensations before general death. The nerves have then but little to transmit, and the brain but little to perceive. As to motion, there is but little in old age, because but little is felt; for feeling and motion are two things that generally follow the same proportion. The brain and the nerves are almost inactive in this respect. The first is not put in action by the intellectual functions; memory, imagination, judgment, attention, &c. all are enfeebled, none are exerted with clearness.

Changes of structure constantly accord with these changes of functions. In the fœtus, the brain is almost fluid; in old age, it is extremely firm. This organ has passed through a variety of gradations between the two extreme ages. We know that anatomists always select the brain of an old person in order to study this viscus, all the parts of which are broken with difficulty. I would observe upon this subject, that what is natural at this age, indicates in a young person a morbid alteration. In general, we have not yet sufficiently studied the comparative anatomy of the different ages, to make applications of it to the examination of dead bodies.

The vessels diminish in the brain in proportion as its hardness increases. In this respect it has an inverse arrangement at the two extreme ages of life. Its colour becomes more dull in old age. It is rare that it is ossified; there are, however, some examples of it. The phenomena, that the action of different re-agents presents, are very much slower in taking place than in the adult and especially in the infant. The solution by alkalies is a remarkable proof of this.

We cannot doubt but that this organic state of the brain in old age, has much influence upon the preceding phenomena; to this must be referred the less acuteness of pain at this age. A cancerous tumour of an old person, exactly analogous in its position, form, size and nature to that of an adult, produces much less suffering. Cancers of the womb, the stomach, the breast, &c. furnish examples of this. All the local causes of pain show also the same thing. In the numerous experiments I have made upon living animals, I have uniformly observed, that young ones, when the sensible parts are cut, give signs of the most acute pain; whilst old ones show infinitely less expression of it under similar circumstances. I would make one other remark upon this subject; it is that the variety appears in dogs, in a certain degree to have an influence upon the acuteness of their sensations. All the large varieties make but little noise, and are not much agitated, when their skin, their nerves, &c. are cut; whilst all the small ones, though they may be old, struggle, are agitated, and manifest upon the slightest cause, the most acute sensibility.

As to the influence of age upon pain, it is not astonishing that the animal sensibility having become very obscure in a natural state, should preserve the same character in disease. An old person suffers then much less than the adult, and especially than the infant, under the influence of the same causes; it is a compensation for the diminution of their enjoyments. The infant finds in every thing that surrounds him, a cause of pleasure or of pain; thus smiles and tears succeed each other a hundred times a day upon his little face. An old person on the contrary is always calm; indifference is his natural state.

The nerves experience the same changes as the brain; they harden gradually with age; however their proportion of hardness in the first and last ages is much less remarkable than that of this organ; this arises from the nervous coat; for the effect upon the medullary substance appears to be the same. This medullary substance has appeared to me to be less abundant in the optic nerve of an old person; however it is difficult to determine the quantity. The colour of the nerves becomes dull, like that of the brain. They receive fewer vessels. They are never ossified.

Sometimes we say that the extremities of the nerves have become callous; it is a vague expression, to which no meaning can be attached. When will medical language cease to refer to the empty and inaccurate hypotheses that formerly constituted medicine? Most of these hypotheses have passed away, yet the names to which they gave birth remain.

The nervous system and the brain frequently lose beforehand, in old people, a part of their functions; hence hemiplegia is almost as frequent at that age, as convulsions which are its opposite, are in infancy. It is necessary to distinguish the hemiplegias of old people from those of adults. They are of the same nature as the blindness, the deafness of old people; the difference is only in the injury of sensation or motion.

NERVOUS SYSTEM OF ORGANIC LIFE.

GENERAL REMARKS.

No anatomist has yet considered the nervous system of the ganglions in the point of view in which I shall present it. This point of view consists in describing each ganglion as a distinct centre, independent of the others in its action, furnishing or receiving particular nerves as the brain furnishes or receives its own, having nothing in common, except by anastomoses, with the other analogous organs; so that there is this remarkable difference between the nervous system of animal life, and that of organic life, viz. that the first has a single centre, and that it is to the brain that every kind of sensation comes, and that it is from it every kind of motion goes; whilst in the second, there are as many little separate centres, and consequently little secondary nervous systems, as there are ganglions.

We know that all anatomists, even those who, without affixing to the expression any very definite meaning, have called the ganglions little brains, have taken them for dependancies, for enlargements of the nerves, in whose course they are found; and as most of them are met with in the great sympathetic, they have presented them as a distinctive character of this nerve. But from the general idea I have just given of the ganglions, it is evident that this nerve has no real existence, and that the continuous thread that is observed from the neck to the pelvis, is nothing but a succession of nervous communications, a series of branches that the ganglions placed above each other, send reciprocally to each other, and not a nerve going from the brain or the spine.

The first considerations that induced me to think that the great sympathetic is not a nerve like the others, but a series of anastomoses, were the following. 1st. These communications are often interrupted, without any inconvenience, in the organs to which the great sympathetic goes. There are subjects, for example, in whom is found a very distinct interval between the pectoral and lumbar portions of this pretended nerve, which seems cut in this place, because the last pectoral ganglion and the first lumbar do not send branches to each other. I have often seen also the sympathetic nerve cease, and afterwards appear again between two ganglions and from the same cause, whether in the loins, or in the sacral region. 2d. Every one knows that the opthalmic ganglion, the spheno-palatine, &c. are constantly distinct, and that they do not communicate by their branches except with the cerebral nerves. It uniformly happens that there is between them and those of the great sympathetic, what we sometimes see between these last, viz. a complete deficiency of communication. 3d. In birds, as has been observed by Cuvier, the superior cervical ganglion is also found constantly distinct; it never communicates with the inferior. The filament which in quadrupeds descends the length of the neck, is wanting in them. In many other animals we frequently find interruptions in this succession of anastomoses of ganglions, which constitute what is called the great sympathetic. 4th. The communications of the ganglions are usually made by a single branch; but sometimes many go from one of these organs to the other, so that if the great sympathetic was a nerve like the others, it would present, in this respect, an arrangement wholly different from that of the cerebral nervous system. 5th. Whence does the great sympathetic arise? From the sixth pair? But all the nerves diminish as they go from the brain towards the organs; but this presents then an arrangement entirely different; it increases as it sends off branches. Does it arise from the spinal marrow? But then the branches with which it furnishes a region would come from the branches that it receives from the spinal marrow in this region. Thus the great and small splanchnic would arise from certain intercostal pairs, now they are evidently much larger, the first especially, than the sum of the branches from which they would derive their origin. Observe then that all anatomists have been of a different opinion upon the origin of the great sympathetic. How could they agree upon a thing that has no real existence?

These different considerations render probable the opinion that I have entertained for some time, that the great sympathetic nerve does not really exist, that this cord is but a succession of communications between little nervous systems placed above each other, and that it is not essential that these communications should exist, as is seen constantly between the ophthalmic ganglion and the spheno-palatine, between that and the superior cervical, of which many animals furnish examples. Then I began to regard each ganglion as a separate centre of a little nervous system, wholly different from the cerebral, and distinct even from the little nervous systems of the other ganglions. By considering the functions of the nerves going from these centres, I became more and more convinced that they did not belong to the cerebral system. In fact, these nerves have properties very different from theirs, as we shall see; they do not serve for sensations; they have uniformly no connexion with voluntary locomotion; we see them only in the organs of internal life; hence why they are found concentrated in the trunk, in the thorax and abdomen particularly; why they are not met with in the head, where almost all the organs belong to animal life; why they are not seen in the extremities, which are exclusively dependant upon this life.

Distributed almost every where to the organs of the internal life, the ganglions and their nerves derive their character from it; and this is it. 1st. They are not symmetrical; thus the nerves of all the plexuses of the abdomen, those of the cardiacs, &c. have a remarkable irregularity. 2d. There are numberless varieties in the form of these plexuses and in that of the ganglions; it is thus that, sometimes lenticular, sometimes triangular, sometimes divided into many portions, that which is under the diaphragm is never seen twice alike. Hence the error of every name derived from the figure; a remark that is applicable generally to the organs of internal life. We might rather borrow the names of forms for animal life in which these forms are more invariable. On the other hand, the existence of many ganglions varies; sometimes there are three of them in the neck, at others but two. The arrangement of one side does not produce a similar one on the other. I have frequently remarked that the number of filaments arising from the superior cervical ganglion differs very much from those that take their origin from the opposite side. There are two analogous organs at each side; but several attributes of structure destroy the general character of symmetry; it is like the lungs and the kidnies. We can, then, establish as a distinctive character between the two nervous systems, the symmetry of one and the irregularity of the other; now, this character is one of those which distinguish the two lives, as I have remarked before.

From all this it is evident that a line of demarcation separates the nerves of the ganglions and those of the brain, and that the method is inaccurate which considers them as forming a single nerve, arising by some origin from this last. Their communications no more prove it to be a general nerve, than the branches which pass from each of the cervical, lumbar, or sacral pairs, to the two pairs that are superior or inferior to it. Notwithstanding these communications, we consider each pair in a separate manner, and not as one nerve by their union. So that each ganglion should be described separately, notwithstanding the branches it sends to others.

The description of the system of the ganglions should be analogous to that of the cerebral nerves. For example, I describe first the lenticular ganglion, as was done for the brain; then I examine its branches, among which is found the great splanchnic; for it is very improper to say that this nerve gives origin to this ganglion. The same in the neck, in the head, &c. each ganglion is first described; then I treat of its branches, among which are found those of communication. There are, then, almost as many descriptions as there are separate ganglions. For example, we ought not to treat of the ophthalmic nerve with the common motor; to be convinced of this, it is sufficient to see how much the ciliary nerves differ from the others, which, belonging to animal life, are also contained in the orbit.

From all that has been said, it is evident that there are two things to be examined in the nervous system of organic life, 1st. the ganglions; 2d. the nerves that go from them.

ARTICLE FIRST.

OF THE GANGLIONS.

I. _Situation, forms, relations, &c._

The ganglions are little reddish or greyish bodies, situated in different parts of the body, and forming so many centres, from which goes an infinite number of nervous ramifications. Their position most generally is along the vertebral column, where are seen successively below each other, the superior and inferior cervical, the intercostal, the lumbar, and the sacral. It is these especially whose communicating branches form the great sympathetic. But besides these ganglions, which are placed as it were in a row, we find many separate ones in different parts, as the ophthalmics, the sphenopalatines, the maxillaries in the head, as also the semilunars in the abdomen. In the thorax there are none thus separate; though sometimes we see a small one at the base of the heart.

Besides the ganglions uniformly seen, there are often accidental ones, if we may so say; such are those that are sometimes found in the hypogastric plexus, in the solar even, at some distance from the semilunar, in the middle part of the neck, &c. On the other hand, some of those that are usually met with are oftentimes not found, as some of the lumbar, sacral, maxillary, &c.; so that it appears that there is really an essential difference between the ganglions under the relation of existence. The superior cervical, the semilunar, the ophthalmic, &c. are always found; they appear to be essentially necessary to the action of the organs to which they furnish nerves. Most of the others may be wanting on the contrary, and be supplied by those of the neighbouring ones, or by others formed not in the ordinary anatomical order.

All the ganglions are generally in a deep situation. Destitute of a bony covering analogous to that of the brain, they are not less powerfully protected against the action of external bodies. It is this deep position, that prevents us from making experiments upon almost all of them, from making those at least which require that the animal should live a certain time after they have been made. It is this which will undoubtedly keep up for a length of time the obscurity that hangs over the functions of these organs.

The form of the ganglions is extremely irregular. In general they are round; but sometimes they are long, as the superior cervical; sometimes the ganglion is a species of triangular body, with obtuse and round ends, as the ophthalmic; sometimes the form is semilunar, like that which has this name, &c. Generally these forms are very variable, as I have said; the most uniform is that of the superior cervical.

Embedded in a quantity of cellular texture, all the ganglions are separated by it from the neighbouring organs. Almost all of them are so disposed, that they experience but little motion from these organs, and cannot receive it from any of the vessels that enter them. Those situated along the vertebral column especially, present this phenomenon, very different from that which takes place at the brain, whose functions are essentially connected with the constant agitation that the blood imparts to it, and very different from that which we observe in the plexuses of nerves coming from these same ganglions.

II. _Organization._

The ganglions have generally in the adult a reddish colour very different from that of the nerves; sometimes they are greyish. When opened, they present a soft, spongy texture, resembling considerably at first view that of the pretended lymphatic glands.

This texture has nothing in common with the cerebral substance, nor with that which occupies the canal of the nervous coat. These two last should rather be ranked in the class of fluids, as I have said; their substance is a pulp, a real jelly. Thus they have not any of the properties of solids. They do not harden like horn; the kind of hardening, the result of the contact of alkohol, of the acids, and of caloric, is wholly different from the horny hardening. It is analogous to the hardening of the white of an egg. On the contrary, the texture of the ganglions hardens like horn in an evident manner, a phenomenon which is characteristic of all the solids, except the epidermis, the nails, and the hair, which make a separate class. Treated by the acids, the ganglions, after wrinkling, hardening like horn and hardening gradually, soften and become fluid.

Boiling produces a phenomenon nearly analogous; 1st. horny hardening and hardening at the instant the water boils; 2d. continuance of this state for half an hour; 3d. softening gradually brought on; when this last is complete, the effect of the boiling is finished. In this state, the ganglions are all different from the nerves submitted to the same experiment. I have observed also in veal, that they have a very different taste from that of the nerves, a method of research which should not be neglected in attempting to ascertain the difference of the nature of the organs. In fact, as we do not yet know the difference of the principles which enter into the composition of each, we should be satisfied with the difference of the qualities.

The alkalies act a little upon the ganglions, which they tend to dissolve, and which they do partly dissolve, if they are very caustic. But this solution is infinitely less prompt and less easy than that of the cerebral pulp by the same re-agents. The ganglions resist putrefaction as much and even more than the nerves; this forms also a very remarkable difference between them and the cerebral substance. In general, we cannot establish any kind of analogy between them.