89 Many of the bodies represented as granule and colloidal cells are in reality round spheres of myelin, whose resemblance to a nucleated cell is sometimes heightened by their occasional inclusion of a fragment of an axis-cylinder which has not yet lost its power of imbibing carmine and other dyes. Where softening has proceeded farthest, there the spherical and other forms of myelin are found crowding the field, and mingled with them are blood-corpuscles, fragments of blood-pigment, granular detritus, and bodies known as fatty granular cells. A number of bodies of very different origin have received this name, some of them, like the fragments of myelin alluded to, not even meriting the name of cells. Others, however, are veritable formed histological elements, either leucocytes or cellular ingredients of the neuroglia, which, having fed on the products of myelin disintegration, have become enlarged and coarsely granular. The longer the duration of the process the more numerous are these bodies, showing that they are not the coarse and essential factor of the inflammation, but an accompaniment, subserving some conservative process, inasmuch as they either remove effete material or contribute to the permanent organization of the cicatricial or atrophic tissue.
The period now reached by the morbid process may be regarded as a sort of interregnum. The necrotic tissues have not yet disappeared on the one hand, the products of inflammation have not yet organized themselves on the other. It is in this period that the ganglionic elements are described as undergoing certain changes in outline and in appearance. Above all, one change has interested observers, which, consisting in the development of what appear to be spherical vacuoles in the interior of the cell, is termed vacuolization. I can compare it to nothing so nearly as to the appearance which is produced by the formation of gas-bubbles in a putrefying albumen or other semifluid substance.
This vacuolization of ganglion-cells is now regarded as a cadaveric change. It is not agreed, as yet, whether its occurrence in myelitis is so frequent as to suggest its ante-mortem occurrence as a veritable feature of the disease. I have been struck by this change in the neighborhood of wounds artificially produced in dogs, even in the fresh specimen. It must be remembered, however, that under these circumstances, the nutrition of the cell being destroyed and exposure to the macerating effect of the cerebro-spinal and pathologically exuded fluids occurring, a cadaveric change may take place intra vitam.
The influence of phosphorus and alkaloid as well as metallic poisons on the cord has been experimentally studied by a number of observers. Unfortunately, Popow, Tschisch, and Danillo—who described as characteristic a resulting change in the staining reaction of the cells, the development of vacuoli in them, and an atrophy of their processes—had not made a sufficient number of examinations of normal cords under like methods of preparation to recognize which of these deviations is without the physiological confines. Kreyssig90 demonstrated the existence of all these conditions in the cords of perfectly healthy animals preserved in chromic acid;91 and Schultze confirms him, and expresses a surprise, which must be shared by all reflecting investigators, that poisons of so widely different a character should have an identical effect on the cord-substance, as is claimed by the writers named.
90 Virchow's Archiv, cii.
91 He attributes the remarkable difference in staining of nerve-cells of the same ganglionic group and in the same section to the sudden transferral of the hardened specimens to strong alcohol, which seems to be the custom in some German laboratories. He claims that uniformity in staining is effected if the specimen be transferred from the chromic preparation to weak alcohol, then to stronger, and thus by gradual increase of the strength to strong spirit. Possibly, instead of approximating the real structural indications by this method, Kreyssig may obliterate them. In specimens which alcohol is not permitted to touch before staining is completed, very deeply and very lightly stained cells will be found almost side by side. The shorter the hardening process, the more perfect the staining method, the more likely are these differences to be found. It is reasonable to assume that the difference in dye-absorbing power indicates slight differences in the cell-protoplasm, marking the nutritive state of the latter and occurring within physiological limits.
If life be prolonged and the conservative processes assert themselves, the disintegrated material disappears, and as the white color of the greater area of the cord was due to the myelin, and the latter has now become destroyed within the diseased area, the latter presents a grayish color. This phase is often termed gray softening. The consistency is, however, much firmer than in the previous stage. Trabeculæ of connective tissue form, enclosing in their meshes a large number of neuroglia-nuclei and sometimes spaces filled with fluid. According as condensation and retraction or rarefication preponderate the process will terminate either in the formation of a sclerotic focus or of a cyst. Occasionally an irregular spongy tissue containing several small cysts results.
Charcot claims that a restitution of anatomical continuity, and therefore of physiological potentiality, may occur in a myelitic cicatrix. But the experiments of Kahler92 and Homén93 prove that when a nerve-tract is once destroyed within the spinal cord all hope of restoring that tract in structure, and thus to restore its functions, is at an end. Unlike the fibres of the peripheral nerves, those of the spinal cord and brain do not seem capable of regeneration.94 If a restoration of function is to occur at all, it must occur through other channels than those destroyed—in other words, by vicarious action.
92 Prager medizinische Wochenschrift, 1884, No. 31.
93 Contribution expérimentale à la Pathologie et à l'Anatomie pathologique de la moelle épinière, Helsingfors, 1885, abstracted in Centralblatt für die medizinisches Wochenschriften, 1886, No. 16.