AQUEOUS extracts of mammalian testicle contain a factor that dramatically increases the permeability of the tissues to injected fluids [McClean, 1930;Hoffman & Duran-Reynals, 1931]. This can be demonstrated by the rapid disappearance of the bleb following intracutaneous injection of these extracts and by the rapid spread through a large area of skin of any suitable coloured indicator that may be injected together with them. This factor is associated with the germinal epithelium and can be extracted from spermatozoa [McClean, 1931]. Factors with similar diffusing properties have been obtained from the most diverse sources, for example, from ifitrates and extracts of staphylococcus and streptococcus [Duran.Reynals, 1933], from organisms of the gas-gangrene group and virulent pneumococci [McClean, 1936], from extracts of malignant tissues [Duran-Reynals & Stewart, 1931; Boyland & McClean, 1935], from snake and spider venoms [Duran-Reynals, 1939] and'from leeches [Claude, 1937].Various methods for the partial purification of testicular extracts and of baclFrial culture ifitrates of the gas-gangrene group have been described [Morgan
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