§ 700. Pathological Changes.—Kobert and Küssner observed that when oxalate of soda was subcutaneously injected into animals, there was often abscess, and even gangrene, at the seat of the injection. If the poison were injected into the peritoneal cavity, death was so rapid as to leave little time for any coarse lesions to manifest themselves. They were not able to observe a cherry-red colour of the blood, nor did they find oxalate of lime crystals in the lung capillaries; there were often embolic processes in the lung, but nothing typical. They came, therefore, to the conclusion that the state of the kidneys and the urine was the only typical sign. The kidneys were dark, full of blood, but did not show any microscopic hæmorrhages. Twelve hours after taking the poison there is observed in the cortical substance a fine striping corresponding to the canaliculi; in certain cases the whole boundary layer is coloured white. If the poisoning lasts a longer time, the kidneys become less blood-rich, and show the described white striping very beautifully; this change persists several weeks. The cause of this strange appearance is at once revealed by a microscopical examination; it is due to a deposition of oxalate of lime; no crystals are met with in the glomerules. Both by the microscope and by chemical means it may be shown that the content of the kidney in oxalates is large.[695] So far as the tissues generally are concerned, free oxalic acid is not likely to be met with; there is always present sufficient lime to form lime oxalate. The urine was always albuminous and contained a reducing substance, which vanished about the second day after the dose. Hyaline casts and deposits of oxalates in the urine never failed.[696]
[695] The important fact of the oxalate-content of kidneys and urine, and the expulsion of casts, was first observed by Mitscherlich in 1854. He noticed in a rabbit, to which had been given 7·5 grms. of oxalic acid, and which had died in thirteen minutes, “renes paululum magis sanguine replete videbantur, in urina multa corpora inveniebantur, quæ tubulos Bellenianos explese videntur” (De acidi acetici, oxalici, tartarici, citrici, formici, et boracici, &c., Berlin).
[696] Rabuteau has discovered by experiment that even the oxalates of iron and copper are decomposed and separated by the kidneys. Gaz. Méd. de Paris, 1874.
§ 701. Observations of the pathological effects of the oxalates on man have been confined to cases of death from the corrosive substances mentioned, and hence the intestinal tract has been profoundly affected.
In the museum of St. Thomas’ Hospital is a good example of the effects produced. The case was that of a woman who had taken a large, unknown quantity of oxalic acid, and was brought to the hospital dead. The mucous membrane of the gullet is much corrugated and divided into numerous parallel grooves, these again by little transverse grooves, so that the intersection of the two systems makes a sort of raised pattern. It is noted that in the recent state the mucous membrane could be removed in flakes; in the upper part it was whitish, in the lower slate-coloured. The stomach has a large perforation, but placing the specimen beside another in the same museum which illustrates the effect of the gastric juice, in causing an after-death solution of a portion of the stomach, I was unable to differentiate between the two. The mucous membrane had the same shreddy flocculent appearance, and is soft and pale. The pyloric end is said to have been of a blackish colour, and no lymph was exuded.
§ 702. The pathological changes by the acid oxalate of potash are identical with those of oxalic acid, in both the gullet and stomach being nearly always more or less inflamed or corroded; the inflammation in a few cases has extended right through into the intestinal canal; there are venous hyperæmia, hæmorrhages, and swelling of the mucous membrane of the stomach. The hæmorrhages are often punctiform, but occasionally larger, arranged in rows on the summits of the rugæ; sometimes there is considerable bleeding. In the greater number of cases there is no actual erosion of the stomach, but the inner layer appears abnormally transparent. On examining the mucous membrane under the microscope, Lesser[697] has described it as covered with a layer which strongly reflects light, and is to be considered as caused by a fine precipitate of calcic oxalate. Lesser was unable to find in any case oxalic acid crystals, or those of the acid oxalate of potash. There are many cases of perforation on record, but it is questionable whether they are not all to be regarded as post-mortem effects, and not life-changes; at all events, there is little clinical evidence to support the view that these perforations occur during life. In the case (mentioned ante) in which death took place by coma, the brain was hyperæmic. The kidneys, as in the case of animals, show the white zone, and are congested, and can be proved by microscopical and chemical means to be rich in oxalates.
[697] Virchow’s Archiv, Bd. lxxxiii. S. 218, 1881.