Fibrillae of Cells. A Need for Further Investigation *

Very often the student in histology, as well as the more advanced worker in this field, finds the subject of fibrillae in cells somewhat difficult and confusing. In spite of the fact that fibrillae have been the subject of investigation for many years, authorities are not agreed concerning the structure or function of these cellular elements, and there are still some who have doubts as to their actual existence. There are, on the one hand, those who are certain that they are fundamental constituents of protoplasm and that they function as supporting structures; and it was Heidenhain' who called such supporting or skeletal structures tonofibrillae. On the other hand, there are individuals who are convinced that these structures are filamentous mitochondria or are merely products of biochemical procedure in the nature of fixative artifact. It has also been said that they are the seat of the essential energies upon which life depends. A few of the names associated with the early studies in this field are: Heitzmann, Klein, Leydig, Flemming, Carnoy, Van Beneden, Retzius, and Heidenhain (Wilson"6). These writers regarded the fibrillae as an essential feature of the protoplasmic structure playing a leading role in the protoplasmic activities. The structures termed fibrillae, and there are numerous kinds known as tonofibrils, neurofibrils, myofibrils, ergastoplasmic fibrils, are, therefore, described as characteristic and prominent elements of certain cells. They are seen in muscle and nerve cells, as well as in epithelial cells such as the prickle-cell layer of the stratified squamous epithelium of human skin. Fibroblasts and other cells are believed to show these structures and they can be studied quite easily in iron-alum hematoxylin-stained material. In the prickle-cells these structures seem to pass from cell to cell through what may be called protoplasmic bridges. In gland cells fibrillae form a widespread and conspicuous feature and are considered