Chemical nature of the first products (nuclei) of the argyrophil staining.

In agreement with LIESEGANG (1911) but in disagreement with VOIGT (1957), PARTRIDGE (1957) and WINKELMANN and SCHMIT (1959), the first product in the majority of the traditional argyrophil methods is submicroscopic grains (nuclei) of metallic silver forming in the impregnating bath at the effect of reducing groups of the tissue (argyrophil I reaction). It is the localization pattern of the metallic silver nuclei that determines the distribution of the silver in the final microscopic image, and not the colloid character of the tissue, as stated by VOIGT (1952) and others. In special cases, colloid grains of certain silver compounds (non-metallic silver nuclei) forming with the contribution of the tissue (argyrophil II reaction) in the impregnating bath constitute the basis of the staining. There are argyrophil methods which consist of pretreatments and a physical development but have no impregnation phase. In one part of them, non-metallic silver nuclei forming with the contribution of the tissue (argyrophil II reaction) in the physical developer, in the other part, certain points of the tissue structure with favourable chemical composition, capable of catalyzing the interaction of silver ions and the reducing component of the physical developer (argyrophil III reaction) serve for the initiation of the staining.