The different types of fibres of the collagenous and elastic systems can be demonstrated specifically in tissue sections by comparing the typical ultrastructural picture of each of the fibre types with studies using selective staining techniques for light microscopy. A practical modus operandi, which includes the recommended staining procedures and interpretation of the results, is presented. Micrographs and tables are provided to summarize the differential procedures. Reticulin fibres display a distinct argyrophilia when studied by means of silver impregnation techniques, and show up as a thin meshwork of weakly birefringent, greenish fibres when examined with the aid of the Picrosirius-polarization method. In addition, electron-microscopic studies showed that reticulin fibres are composed of a small number of thin collagen fibrils, contrasting with the very many thicker fibrils that could be localized ultrastructurally to the sites where non-argyrophilic, coarse collagen fibres had been characterized by the histochemical methods used. The three different fibre types of the elastic system belong to a continuous series: oxytalan-elaunin-elastic (all of the fibre types comprising collections of microfibrils with, in the given sequence, increasing amounts of elastin). The three distinct types of elastic system fibres have different staining characteristics and ultrastructural patterns. Ultrastructurally, a characteristic elastic fibre consists of two morphologically different components: a centrally located solid cylinder of amorphous and homogeneous elastin surrounded by tubular microfibrils. An oxytalan fibre is composed of a bundle of microfibrils, identical to the elastic fibre microfibrils, without amorphous material. In elaunin fibres, dispersed amorphous material (elastin) is intermingled among the microfibrils.

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The influence of tissue section thickness on the color and intensity of birefringence displayed by collagen in tissue sections studied by means of the Picrosirius-polarization method, is reported in this paper. When dermal collagen sections of different thicknesses (ranging from 0.25 to 11 micrometers) were studied by this method, it became evident that not only did the intensity of birefringence increase proportionally to tissue section thickness, as was to be expected, but also a gradual shift in color from green through a yellow to red could be observed as tissue section thickness increased. The limitations of the Picrosirius-polarization method for the localization of collagen types I, II, and III in routinely used histological slides is discussed, showing that this method is useful for the study of the distribution of the different types of interstitial collagen in normal adult vertebrate organs.

A morphologic study of the structure of the tail fin in eight species of teleosts was performed by aid of the Picrosirius-polarization method, which is a specific histochemical method for the detection of collagen in tissue sections. This structure is composed mainly of skeletal elements, the fin rays, covered by skin. Fin rays are bound to each other and to the surrounding tissues by a series of collagenous ligaments forming a complex, highly pliable and resistant structure. Although the general structural pattern of tail fins was consistent in all species studied, the comparative aspects reported in this paper show that variations in the form and size of their components are responsible for the morphologic diversities which are closely related to specific functional adaptations. Morphometric data on the number and size of actinotrichia in normal adult specimens are presented.

A correspondence between the appearance of vaginal smears and the layers of the epithelium from which the cells had desquamated was established in untreated rats during the estrous cycle, in control ovariectomized rats and in spayed rats injected with either estrogen or progesterone. The technique for preparing and staining the smears (modified Shorr’s staining procedure) is outlined. A simplified.system of classification which allows the accurate identification of the various stages of the reproductive state in the rat is described. Standing estrus, as well as the influence of estrogen on spayed rats, is characterized by marked cornification of the cells and the disappearance of leukocytes. At the end of estrus, the cornified layer is sloughed off and invasion by leukocytes occurs. During diestrus, as well as in untreated ovariectomized rats, the vaginal contents consistently lack cornified cells whereas leukocytes are very plentiful. Proestrus follows diestrus: the vaginal smear is devoid of leukocytes and characterized by nucleated epithelial cells. Pregnancy, as well as the influence of progesterone on ovariectomized rats, is also characterized by epithelial growth and desquamation but at different rates, resulting in the presence of intermediate cells, and polymorphs and mucus forming a noticeable background to the smear. Since vaginal smears display cell pictures characteristic for each hormone after administration of estrogen or progesterone, exfoliate cytology is a good indicator of the stage of the reproductive state in the rat.

The results presented in this paper show that collagen fibers can be clearly distinguished from reticular fibers using the picrosirius-polarization method. A morphologic and morphometric study of these two types of fibers with electron microscopy shows that reticular fibers are characterized by the smaller diameter of their fibrillar components and the higher content of interfibrillar material, resulting in a loose arrangement of the fibrils. The evidences presented suggest that the amorphous matrix in which fibrils are embedded is responsible for the silver impregnation of reticular fibers. Our results show that the matrix of reticular fibers is characteristically rich in heparitin sulfate, and that the glycosaminoglycans present show a high interaction with the fibrillar component of these fibers.

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