The mechanism of silver staining.
Though much research has been devoted to the elaboration of silver stains for nervous tissue, there have been few experimental investigations of the mechanism of the staining process. Liesegang (1911) claimed that during the impregnation in the silver bath, ultramicroscopic particles of metallic silver were deposited in the sections as silver 'nuclei', and it was on these 'nuclei' that further silver deposition occurred during development. Thus the final staining of the tissue was determined by the initial distribution of the silver 'nuclei'. This theory was generally accepted until Owens & Bensley (1929) and Nageotte & Guyon (1930) suggested that the staining was more dependent on the physical properties of the tissue. Zon (1936) concluded that the differences in stainability of the tissue elements were due solely to the differences in the protective properties of their colloids, which permitted varying degrees of precipitation of silver within them. Silver (1942) thought that during the development phase of silver staining negatively charged silver micelles were formed and these were precipitated by the positive charges carried by the tissues. The pH of the silver solution was important only in so far as it affected the charge on the micelle, rendering it more or less liable to flocculation, but the pH of the developing solution was of extreme importance in so far as it affected the charge on the tissues and hence the distribution of the silver. As none of the previous opinions seemed to be based on incontestable evidence, it was considered that a further investigation into the mechanism of silver staining might throw further light on the problem.
The Physical Chemistry of Silver Staining
It has been shown that silver deposition plays a part in the silver staining process. From this it has been concluded that the rate of reduction of silver within and on histological structures is an important factor.Some factors controlling the rate of reduction, such as the adsorption of silver hydroxide and ammonia, the affinity of silver for proteins, and the protective power of the gel structures have been pointed out.Some simple applications of the ideas to silver staining have been given and two technics described, one making use of piperidine instead of ammonia, the other carrying out the reduction in the presence of the silver solution to facilitate deposition.
Preparation of hydrophilic poly(vinyl butyral) hollow fiber membrane via thermally induced phase separation
Abstract Hydrophilic microporous hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and three kinds of polyethylene glycols (PEG) with the molecular weight of 200, 400 and 600 were used as polymer and diluents. In all cases, liquid–liquid (L–L) phase separation occurred and asymmetric cellular structures with the smaller pores at the outer surface were obtained. The properties of membranes such as pore size, water permeability, solute rejection and intensity were investigated by changing molecular weight of PEG, concentration of PVB, composition of the bath and air gap distance. The smaller molecular weight of PEG, the more PEG in the bath and the shorter air gap distance resulted in the higher water permeability, the lower solute rejection property and the lower mechanical strength.