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fibrillar network about the nucleus of each cell. On page 85 he figures two cells showing such perinuclear networks and states in the text: "Von der Existenz glatt durch die Zellen hin. durch passierender Neurofibrillen habe ich mich allerdings an diesem Object (palate of frog) nicht mit Sicherheit überzeugen können. Es ist aber doch sehr wohl möglich dass auch hier solche vorkommen, doch ist ihre Zahl sicher nicht gross." To me it seems evident both from BeThe's figures and my own preparations that most of the fibrillae do pass directly through the cells. The doubtful point is in the existence of a perinuclear network. The structures figured by BETHE could easily be accounted for by the adhesion of the fibrils at their points of division. BeThe's figures show plainly that the main portion of each fibril passes through the cell. It is only small side branches which show the semblance of a network. Of this I am sure, that in all my preparations of these cells the fibrillae do not form a network about the nucleus. The usual condition found in these cells from the palate of the frog is shown in fig
The fibrils often divide in the region of the nucleus, but the branches which thus arise are not continuous with each
Fig. 7. A single cell from the subepithelial network in the palate of Necturus; most of the fibrillae run straight through the cell but in the region of the nucleus there is apparently evidence of a network. X 1000.
other. It is possible that the network figured by BETHE may not have been stained in my preparations; but as the fibrillae passing through the cells were clearly demonstrated, it seems strange that some trace of the network, if present, could not
be discovered. In the palate of Necturus there was some evidence of a fibrillar basket-work about the nuclei of certain cells (Fig. 7). Only a few meshes were observed and these may have been formed by the crossing of fibrillae; by far the greater number pass directly through the cell without branching, as may be seen in the figure. I therefore maintain that these cells, if nervous structures, are to be compared, not as BETHE would have us, to the ganglion cells of invertebrates (in which a complete basket work is formed by the fibrillae), but rather to the central nerve cells of vertebrates, through which, as a rule, most of the neurofibrillae pass entirely independent of each other.
In the palate of the frog the cells of the networks are usually located centrally with reference to the fibrillae, the nucleus being surrounded by the latter. It is difficult to see how such nuclei can be interpreted as belonging to sheath cells. Often, how ever, a cell lies eccentric to the fiber, the fibrillae all passing to one side of the nucleus; or two nuclei may be found in close proximity to each other, the one surrounded by fibrillae, the other being eccentric in position.
The form of the nuclei also varies with their location. If surrounded by fibrillae the nucleus may be of spheroidal or pyramidal shape; if lying eccentric they are usually flattened and elongate in form.
I have described in some detail these networks of cells and fibers both because my observations substantiate more or less completely the results of DogieL, BETHE, and LEONTOWITSCH, and in order that the significance of the following degeneration experiments might be more easily understood. From the histological evidence one must conclude that the non-medullated fibers of all these networks are true nervous structures, and not connective tissue as has been maintained. They are composed of neurofibrillae, are connected with medullated fibers, and are not demonstrated by specific connective tissue stains. The presence of neurofibrillae about the nuclei of some of the cells would indicate that they also are of nervous character, as BETHE and LEONOWITSCH assert.
The evidence as to the presence of neuro-fibrillar networks in these cells is not conclusive,
and those eccentrically located might well be sheath cells. The nature of these cells therefore is not definitely settled, and is a problem of great importance. For if it is conclusively proved that they are nerve cells, the structural independence of the neurone and its genesis from a single ganglion cell can no longer be maintained. By a series of degeneration experiments I have attempted to solve the problem.
2. THE RESULTS OF DEGENERATION EXPERIMENTS.
If all of the nerve fibres in the palate of the frog are processes of the nerve cells situated either in the brain or in the sensory ganglion of the seventh cranial nerve, they should, when isolated from these cells for some weeks, degenerate completely, being separated from their only trophic centers. If, how ever, there are peripheral nerve cells in the palate, these as well at the fibers connected with them should remain histologically unchanged. To determine which of these assumptions is correct the following method suggested itself: To sever the palatine nerves from all connection with their central cells, and after the expiration of a period sufficient for complete degeneration, to attempt the demonstration of the peripheral networks by means of methylene blue. The chief difficulty connected with this method lies in the well known fickleness of the stain, a factor which might lead to negative results. I therefore experimented with normal animals until I was able to obtain regularly a good percentage of successful preparations. It was found that the subepithelial and perivascular networks take the stain very quickly as they are in close proximity to the blood vessels and capillaries, through the walls of which the stain passes to the other tissues. The chief point in getting good preparations therefore, is the removal and fixation of the tissues as soon as possible after the stain has passed through the capillaries. If one waits until the larger nerves are impregnated, the color will have disappeared from most of the finer elements.
As is well known, methylene blue is a specific stain for degenerated myelin, and BETHE has proved that the neurofibrillae, when degenerate, lose their power of taking up the stain. In methylene blue preparations it is therefore easy to distinguish between normal and degenerate nervous structures.
Fig. 8. Photograph showing operating frame, the method of tying the frog and the point at which the root of the palatine nerve was exposed. About 12 nat. size.
The palatine branch of the seventh nerve passes, as we have already seen, to the roof of the mouth directly anterior to the lateral process of the basisphenoid bone (Fig. 1, page 96). Lateral to the eyeball it is connected with the maxillary branch of the fifth cranial nerve by the Ramus communicans, although, as far as I have been able to discover, no fibres from the trigemus innervate the palate. To make sure however, that the palatine nerve is completely isolated from the brain and sensory ganglia, it must be severed at the points a and b.
The operation is simple and may be performed in the following manner. The frog is tied out back down upon a wooden frame nine inches long, shaped as shown in figure 8. In each of the five extremities of this frame a vertical slit has been cut. Three small blunt hooks attached to ten inch lengths of thread were provided. The mouth of the frog is opened, a hook caught into the upper jaw and the string drawn taut through the anterior slit, as seen in the figure. By means of a second hook the lower jaw is drawn back against the sternum and the cord fastened in one of the posterior slits. The animal is thus held motionless with mouth wide open. With small scissors an incision one-fourth inch long is made along the median line of the palate. One edge of the cut is then carefully lifted with forceps and hooked to one side, the string being drawn through one of the lateral slits. This exposes the palatine nerve at the point where it enters the roof of the mouth.
(Fig, 1. a; Fig. 8). Next a small hooked needle may be passed under the nerve, the blood vessels separated from it and a portion of the nerve removed. Both palatine nerves may thus be severed by making but one incision, and if the operation is carefully performed, without the loss of a drop of blood. In a similar manner the Ramus communicans may be cut at the point b (Fig. 1) by making two small lateral incisions. It is not necessary to sew up the incisions; in fact the thread used in the stitches was found to irritate the animals and in most cases the edges of the wounds were simply drawn together.
Degeneration Experiments. Series 1. This series of operations was practically negative in its results. Eight animals were operated on during the last week in June, 1903. Six died, before the expiration of two weeks, of a skin disease which developed upon all the frogs kept in the laboratory at the time. Of the two surviving individuals only one took the stain, and in this case very incom