In 1994, Madeleine Bastide described experimental models in immunology that were used during the 1980s to investigate high dilution effects on several
biological systems. She classified the available papers in four categories: High dilutions of
antigens; High dilutions of thymus, bursa and other
hormones; High dilutions of
cytokines; Immunopharmacological activity of
silica. The studies about high dilutions of
antigens were not continued after this period, but gave rise to a long process of a series of in vitro models on
antigens and
histamine dilutions, that led to the demonstration of the
biological modulation effects of these preparations on basophil degranulation. During this process, a multi-centre study was performed, with a high degree of reproducibility among different independent laboratories. The studies about high diluted
cytokines,
thymulin and other
hormones opened a new line of scientific investigation, about the regulatory properties of endogenous substances prepared according to homeopathic methods. The most frequently studied substance,
thymulin, when administered to mice at 5cH potency, is able to improve the activity of phagocytes in different experimental situations, such as viral, bacterial and
parasitic infections. The immunopharmacological activity of
silica was demonstrated, at that time, as an in vivo illustration of the homeopathic 'similia principle'. More recently, studies on
silica have assumed another focus: the putative role of
silica as active contaminant present in high dilutions. This paper presents a follow-up summary on these items, considering the evolution of discoveries from 1994 to 2014.