A system of practical medicine. By American authors. Vol. 2

by Unknown

FIG. 1.

To show the position of the punctures required to produce glycosuria, the lobes of the cerebellum are separated. Below are seen the restiform bodies, the divergence of which circumscribes the apex of the calamus scriptorius and the fourth ventricle. The puncture p' produces glycosuria; the puncture p, glycosuria with polyuria; and a puncture a little higher up than p, albuminuria.

PATHOLOGY AND PATHOGENESIS.—Notwithstanding that this disease has been recognized for two centuries and a half, that abundant opportunity has been furnished for its post-mortem investigation, and that experimental physiology has contributed much information bearing upon the subject, its pathology is still undetermined. Experiment has, however, rendered it very likely that all cases of essential glycosuria—that is, all cases in which saccharine urine is not the direct result of over-ingestion of sugar or sugar-producing food—are accompanied by a hyperæmia of the liver. This hyperæmia, with its consequent glycosuria, can be induced by puncturing or irritating the so-called diabetic area¹ in the medulla oblongata. This area corresponds with the vaso-motor centre, and with the roots of the pneumogastric or vagus nerve in the floor of the fourth ventricle; whence it was at first inferred that this nerve is the excitor nerve of glycosuria. It was soon ascertained, however, that when the pneumogastric was cut, glycosuria ensued only when the central end was stimulated, while stimulation of the peripheral portion was without effect. Whence it became evident that this nerve is not the excitor, but the sensory nerve concerned in glycogenesis.

¹ The diabetic area, as marked out by Eckhard, and which corresponds with the vaso-motor area, as defined by Owsjannikow (Ludwig's Arbeiten, 1871, p. 21), is bounded by a line drawn four or five mm. above the nib of the calamus scriptorius, and another about four mm. higher up.

It was also learned in the course of continued experiment that glycosuria resulted upon transverse section of the medulla oblongata, of the spinal cord above the second dorsal vertebra, of the filaments of the sympathetic accompanying the vertebral artery, upon destruction or extirpation of the superior cervical ganglion, and sometimes, but not always, after division of the sympathetic in the chest (Pavy); also after section or careful extirpation of the last cervical ganglion, section of the two nerve-filaments passing from the lower cervical to the upper thoracic ganglion around the subclavian artery, forming thus the annulus of Vieussens,² and after section or removal of the upper thoracic ganglion.

² Cyon and Aladoff, reprint from the Mélanges biolgiques and Bullétin de l'Académie Impériale de Petersbourg, vol. xiii. p. 91; cited by Dr. Brunton in the Lectures named in note on p. 198; also British Medical Journal, Dec. 23, 1871, p. 731.

FIG. 2.

The last cervical and first thoracic ganglia, with circle of Vieussens, in the rabbit, left side. (Somewhat diagrammatic, many of the various branches being omitted.) Trach., trachea; Ca., carotid artery; n. vag., the vagus trunk; n. rec., the recurrent laryngeal; sym., the cervical sympathetic nerve ending in the inferior cervical ganglia, gl. cerv. inf. Two roots of the ganglion are shown—rad., the lower of the two accompanying the vertebral artery, A. vert., and being the one generally possessing accelerator properties; gl. thor. pr., the first thoracic ganglion. Its two branches, communicating with the cervical ganglion, surround the subclavian artery, forming the annulus of Vieussens. sym. thor., the thoracic sympathetic chain; n. dep., depressor nerve. This is joined in its course by a branch from the lower cervical ganglion, there being a small ganglion at their junction, from which proceed nerves to form a plexus over the arch of the aorta. It is this branch from the lower cervical ganglion which possesses accelerator properties, hence the course of the accelerator fibre is indicated in the figure by the arrows. (Modified from Foster's Physiology.)

All these operations paralyze the vaso-motor nerves by which, in health, the blood-vessels of the liver are kept in a state of tonic contraction; hence these vessels dilate when the nerves are cut. From the facts named we also learn the path of the glycogenic influence, which must be from the medulla oblongata into the spinal cord, thence by the filaments of the sympathetic which accompany the vertebral artery into the lower cervical ganglion; thence through the annulus of Vieussens into the first dorsal ganglion; and thence through the prevertebral cord of the sympathetic, and branches not precisely determined, to the hepatic blood-vessels as shown by the dotted line in Fig. 3.