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.
Observations on the silver impregnation of nerve fibres in teeth.
It is widely accepted that small beaded nerve fibrils form a marginal plexus in the predentine parallel to the pulpo-dentinal surface. Whether or not branches from the marginal plexus continue into the calcified dentine, following an intratubular course (Tojoda, 1934), or are situated in the dentine matrix, is uncertain. To examine this problem it was decided to make, in the first instance, a carefully controlled investigation into the method of impregnating nerves in teeth with silver, taking into account Samuel's (1953a, b) recent evaluation of the many factors which influence the mechanism of silver impregnation. In view of the observations made by Weddell, Pallie & Palmer (1954), use was also made of the in vivo and in vitro methylene blue methods (Schabadasch, 1935) as a control for the results of the impregnation with silver.
Microbial flora of frozen tail meat from captive Nile crocodiles (Crocodylus niloticus).
Frozen tail meat samples from nine Nile crocodiles (Crocodylus niloticus) were evaluated for microbial numbers and types. Microbial analyses yielded a mean aerobic plate count (APC, 30 degrees C) of 4.86 log cfu/g, a mean coliform count (TC, 37 degrees C) of 3.77 log cfu/g and a mean faecal coliform count (FC, 44 degrees C) of 3.40 log cfu/g. Salmonella was isolated from three samples, and beta-haemolytic streptococci from two samples. Yersinia, Aeromonas, Staphylococcus aureus and Bacillus cereus were not isolated. Typical bacterial genera recovered included Flavobacterium, Pseudomonas, Acinetobacter, Enterobacter, Moraxella, Micrococcus, Staphylococcus and Streptococcus.