On the nature of the silver reaction in animal and vegetable tissues

Abstract

Though the use of nitrate of silver as a reagent in histology has now a half century of history, and has been of the greatest service in elucidating the structure of some tissues, it has not yet been determined how the reagent is affected by the tissues, or what compound or compounds in the tissues are responsible for the precipitate which becomes discoloured in the sunlight. There are, indeed, references to these points in the literature of the subject, but these are scanty, and they are not at all in accord, while the majority are only guesses or fanciful explanations of the reaction itself. It may even be said that the investigators who used the reagent directed the whole of their energies to determining what it showed from the morphological side rather than what was involved in the reaction itself, and because of this there has been nearly 30 years of discussion on the question whether the results obtained with the reagent were trustworthy or were of the nature of artifacts. The principal value of the reagent to the earlier observers appeared to be the fact that, after impregnation with nitrate of silver, and exposure of the preparation to light, cell outlines were revealed, and thereby the structure of lymphatics and of lymph tissue were demonstrated, the outlines being shown through the brown reaction which they manifested in such preparations. Von Recklinghausen, who was amongst the first to use the reagent for this purpose, held that the silver salt is deposited in what he regards as the cement substance between the cells, and that this cement material under the influence of light reduces the silver. It was pointed that the reaction is not confined to the cell peripheries and intercellular material, for preparations sometimes showed the reaction present in the cytoplasm of the cells, but absent from the membranes and the intercellular structures. This condition was known as the positive reaction or positive image, and was attributed by Schweigger-Seidel to the decomposition and redistribution of the silver precipitate which, in the normal cell giving the negative image, is to be found in the intercellular spaces and boundaries, that is, in the cement substance of Von Recklinghausen. Schweigger-Seidel maintained that the decomposition was brought about by chlorides forming silver chloride from the silver albumen precipitate in the intercellar material, the silver chloride so formed dissolving in the presence of chlorides, and thus diffusing into the cytoplasm, where, under the influence of light, it became the subchloride, and he proved this by taking preparations which had been treated with nitrate of silver, but not acted on by light, and placing them away from the light in a solution of sodium chloride. In these, when reduced by the light, the coloured silver salt or compound obtained chiefly in the cytoplasm. According to Hiiter the positive image may arise through diffusion of the cement substance into the cytoplasm and the consequent intracellular precipitation of the silver compound. His, in 1862, held that the silver compound in the cornea which reduces in light is not an albumin compound, but chloride of silver, for when the cornea was treated with mercuric nitrate, which dissolves chloride of silver, all the silver precipitate was dissolved, which would not have been the case had any of the compound been silver albuminate. In later observations, however, he admits that the silver compounds may be an albuminate as well as a chloride, and that both reduce under the influence of light. A similar view was held by Harpeck, Hartmann, Auerbach, and Henle. Schwalbe found that if the serous membrane to be examined be first washed with a 4-per-cent, sugar solution, treatment with silver nitrate will not bring out the silver lines usually obtained, and he concludes from this that the cement substance, such as Yon Recklinghausen postulates, has nothing to do with the reaction, that the latter is due to an albuminous layer, “ an albu­minous cement substance,” adhering to the edges of the cells, and which can be washed away.