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 area[1] 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 {196} 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. [Footnote 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. [Footnote 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.] [Illustration: 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.)