A histochemical and electron microscopic study on the collagen of nerves in the domestic fowl.

The collagen in the endoneurium is present as argyrophilic reticular fibres, which show up as thin, weakly birefringent greenish fibres when studied by aid of the Picrosirius-polarization method, and are composed of loosely arranged thin collagen fibrils. The epineurium consists of thick non-argyrophilic collagen fibres, which display a strong birefringence of red or yellow colour when studied by the aid of the Picrosirius-polarization method, and consist of closely packed thick collagen fibrils. These characteristics strongly suggest that the reticular fibres in the endo- and perineurium are composed mainly of collagen Type III, whereas collagen Type I predominates in the epineurium. The fact that these observations on birds are consistent with the descriptions available in the literature for fish, amphibians, reptiles and mammals, argues in favour of the existence of a uniform structural pattern of collagen distribution that is a general phenomenon in vertebrate nerves.