The nerve centres undergo profound changes which have been studied by Thanhoffer. The pia mater in the affected parts of the spinal cord is the seat of active congestion and thickening. The central canal of the cord is dilated (syringomyelia) more at one point than another, contains more than the normal amount of liquid, and the neuroglia around it is thickened and fibrous (sclerosed). The substance of the cord, both white and gray, shows congestion, blood staining, at points foci of softening, and at others induration (hyperplasia of the neuroglia). The nerve cells are modified in various ways, some being granular, some discolored by fine granular pigment, some having enlarged and multiplied nuclei, and some show vacuoles. The nerve filaments often show a granular degeneration extending from the nerve cell into the axis cylinder, and the latter is liable to be varicose or uneven in size. In the affected portion of the cord leucocytes are numerous and hyperplasia is often present. The neuroglia especially tends to encrease, and apart from the foci of softening tends to give a special firmness to the substance. At intervals, in the perivascular spaces, may often be found minute (microscopic or macroscopic) blood clots. The subarachnoid and subdural fluid is encreased and may be pinkish. At the roots of spinal nerves, especially in the dorsal and lumbar regions, a gelatinoid exudate may invest the nerve, distending the connective tissue beneath the neurilemma and even occupying the interval between the nerve filaments. Sometimes large corpuscular bodies are found between the nerve fibres.
The cerebral meninges, especially the pia mater, are congested and opaque. Foci of softening are by no means uncommon and the cerebral ventricles contain an abnormal quantity of fluid.
The bony tissue generally has lost its consistency and the medullary matter may be unduly reddened. The large joints contain an excess of synovia somewhat pinkish in color, and the ligaments of the hip joints are often congested, thickened and softened. The articular cartilage may even show patches of blood staining.
The intestines are usually nearly empty, soft, pale and flaccid, and Ruthe has in one case observed rounded ulcers on the mucosa. Fibroid thickening on the peritoneal surface may indicate a previous exudate.
The mesentery is thickened, with infiltration and has a yellowish discoloration and the mesenteric glands are usually enlarged, softened and friable, though sometimes firm and contracted. The lymph glands adjoining the generative organs are often swollen, pigmented and studded with foci of caseation, varying in size from a pea upward.
The liver is softened and congested or fatty. The spleen is small.
The kidneys are usually large, but flaccid, pale and bleached.
The thoracic organs may show little change, though hypostatic inflammation and foci of caseation or suppuration may be present.
The blood is pale and watery and forms a loose, pale, diffluent clot, while there is an extraordinary diminution of red globules and a relatively great encrease of leucocytes.
In advanced stages the muscles are pale, anæmic and shrunken especially those of the hind limbs.