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.