Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/177

Rh that is, surrounded with a sheath, but naked, being transparent, almost gelatinous, and much more minute than most of the primitive tubes. They almost always exhibit longitudinal lines upon their surface, and readily separate into very minute fibres. In their course they are very frequently furnished with oval nodules, and covered with certain small oval or round, more rarely irregular, corpuscles, which exhibit one or more nuclei, and in size almost equal the nuclei of the ganglion-globules.” (Observationes anat. et microsc. de system. nervos. structura. Berol., 1838, p. 5.)!

These corpuscles may at once be recognised, both in Remak’s delineations, and when examined in the natural state, to be cell-nuclei, which are round or oval, and frequently furnished with one or two nucleoli. They are attached to the most minute fibres, and as they are thicker than the fibres, they often appear to be situated only on their outside. Observation, however, does not warrant the conclusion that such is actually the fact. In the secondary muscle-cells (in which the nuclei decidedly lie within the cell) it frequently appears, and especially in the later periods of development, previous to the disappearance of the nuclei, as if the nuclei lay externally to the cell, inasmuch as they become pushed towards the outside. But no doubt the cell-membrane is at the same time elevated upon them, as we saw to be so distinctly the case in the fat-cells. (Pl. III, fig. 10.) Now, these most minute organic fibres, furnished with nuclei, precisely resemble the earlier condition of the white nervous fibres, as they were represented in pl. IV, fig. 8, a 6. Both have the same pale, minutely-granulated appearance, and both present cell-nuclei in their course. The only difference is, that the organic fibres are much more minute and the nuclei smaller. Each single nucleated organic fibre (I do not mean an entire fasciculus of them) corresponds to a white primitive fibre, and is probably, like it, a secondary cell, which has been generated by a coalescence of primary cells, whose nuclei are the nodules described by Remak’s discovery of the peculiar structure of the organic nervous fibres explains an observation previously communicated by me upon some extremely minute, pale, nervous fibres, which did not appear tubular, and were nodulated at different spots, and which I discovered in the mesentery of frogs. No doubt they were organic fibres.