67 Waller, Philosoph. Transactions, 1850, ii. p. 423; Comptes rendus de l'Acad. de Sci., 1852-55.
68 Ranvier, Leçons sur l'Histologie de Système nerveux, Paris, 1878; Von Recklinghausen, Pathologie der Ernahrung, 1883.
Degeneration in the tracts of the spinal cord occurs after various forms of lesion,69 and is similar in its processes to degeneration in the peripheral nerves. The increase in the connective-tissue elements is more noticeable in contrast with the parts unaffected, and from the density of the tract involved the result has been called sclerosis. The recent researches of Homen70 have shown that the process of degeneration begins in the entire length of the affected tract, and does not proceed from the point of lesion onward, as was formerly supposed.
69 See Vol. V., “Myelitis—The Secondary Scleroses,” p. 892; Schültze, Arch. für Psych., xiv. 2.
70 Fortschritte der Medicin, 1885, No. 9.
When a muscle is separated from its connection with the central nervous system, either by a division of the nerve passing to it or by a destruction of the cells in the anterior cornu of the spinal cord from which that nerve arises, it undergoes an atrophy which is peculiar in being immediate and rapidly progressive, thus contrasting strongly with the gradual and slighter atrophy from disuse in cases of cerebral paralysis where the cells mentioned and the nerve-fibres are intact. There is at first a simple diminution in the number of the fibrillæ of which the muscular fibre is made up, together with an increase in the interstitial connective tissue nuclei. Then an albuminoid and fatty degeneration of the muscular elements occurs, with a proliferation of muscle-corpuscles or nuclei, and a gradual absorption of the débris. The interstitial connective tissue then increases rapidly, forming fibrous bands through the degenerated muscle which compress the few muscular fibres remaining, until as a result the muscle is transformed into a mere ribbon of connective tissue without any power of contractility.71 As these changes go on the electrical reactions change, the three degrees of reaction of degeneration corresponding to the three stages of atrophy described.72 These phenomena of nerve- and muscle-degeneration are observed in traumatic or idiopathic neuritis, in acute and chronic poliomyelitis anterior, in general myelitis involving the anterior cornua, and in bulbar paralysis.
71 Hayem, G., Recherches sur l'Anatomie pathologique des Atrophies musculaires, Paris, 1873; Ross, Diseases of the Nervous System, vol. i. p. 238.
72 See Vol. V., “Electric Reactions.”
The influence of the nervous system on the nutrition of the bones has also been ascertained. When a bone is developing, a lesion of the nerve to it, or of the deeper portion of the anterior cornua of the spinal cord from which these nerves arise, will modify and partly arrest its growth. This is often seen in anterior poliomyelitis and in hemiatrophy of the face occurring in children. In the adult a no less marked effect is produced, although the results are less noticeable. A condition known as osteoporosis is caused, consisting of an enlargement of the Haversian canals and an infiltration of fatty matter into them and an actual decrease in all the inorganic constituents of the bone, which loses in weight, becomes thinner and more fragile, so that spontaneous fractures may occur.73 This condition has been noticed more frequently in diseases of the spinal cord than in neuritis; it is said to occur in locomotor ataxia. It has been found in a few cases of long-standing hemiplegia and also in dementia paralytica, no explanation of its pathogeny in these instances, however, being offered. In a case of ataxia with a lesion in the medulla which involved the nuclei of the fifth, ninth, tenth, and eleventh nerves on one side, all the teeth of the upper jaw on that side fell out within a few weeks, those in the lower jaw remaining.74 Changes in the nutrition of the bones have also been recorded in cases of progressive muscular atrophy in the paralyzed limbs.75
73 Weir Mitchell, Amer. Journ. of the Med. Sci., 1873, p. 113; Charcot, Arch. de Phys., 1874, p. 166.