6 Structure of Neurones in Nervous System of White Rat 



The writer has had the opportunity to study the preparations made after the 

 method of Bethe, Dogiel, and Kronthal, and to compare those with his own preparations 

 from the white rat. In these cases, however, the writer was unable to see any fibrillar 

 structure, such as had been described by those writers, but observed only a reticulum 

 producing pseudo- fibrils. Although the reticular structure of the ground substance 

 seems to be characteristic for young and unmodified nerve-cells, nevertheless in the 

 large multipolar cells it has been altered to such an extent as to present a fibrillar 

 appearance such as is seen in axone hillock of the spinal ganglion cells and around the 

 nucleus. This alteration is probably due to growth changes, as was pointed out by the 

 writer (1901^) in an earlier paper. 



So far as my observations go, the fibrillar structure of the ground substance in 

 the nerve-cells of the white rat is merely a modified network, and consequently it can- 

 not be compared with the fibrillar structures described by Bethe and Apathy. 



III. FINER STRUCTURE OF THE AXONES AND DENDRITES 



Both the axones and dendrites are direct prolongations of the cell-body and pre- 

 sent wide variations in their shape, size, and length, according to the cell-bodies from 

 which they arise. 



1. Structure of the axones. — An axone originates, as a rule, from a specially dif- 

 ferentiated portion of the cell-body known as the "axone hillock." The axone hillock 

 appears under the microscope as a cone, being clearly marked off from the surround- 

 ing cytoplasm by the absence from it of the Nissl granules. Under a higher magnifi- 

 cation this area of the axone hillock is seen to be composed entirely of delicate filaments 

 formed by rows of neurosomes and stains more intensely than the rest of the cell (Plate 

 XIII, Fig. 1). These delicate filaments run convergently from the cell-body to the 

 axone and produce well-known radial arrangement of the filaments. These filaments, 

 however, are not real fibrils, but, as has already been mentioned, they are modifications 

 of the reticulum, and the so-called fibrils in this region are connected with one another 

 by the delicate side branches. In other words, the axone, like the cell-body, is composed 

 of a reticular arrangement of the cytoplasm and may be regarded as an extension of the 

 cell-body proper. The ground substance, or the reticulum, of the cell-body, as well as the 

 axone, ^ composed of cyto-microsomes and neurosomes. The neurosomes in the axone 

 seem to be more differentiated than those in the cell-body proper, for they show a 

 stronger affinity for acid dyes, especially in the terminals of the axones. It is inter- 

 esting to note that the pseudo-fibrils in axones are packed very densely, and therefore 

 the real structure of the primitive reticulum is hard to make out. The structure of the 

 axone may be well studied by examining the cross-sections of the terminals (Plate XIII, 

 Figs. 2, 3, 4 ; Plate XIV, Figs. 5, 6.) The neurosomes which form the terminals of the 

 axis cylinder are very conspicuous, both by their size and by the manner in which 

 they stain. The size of the individual neurosome in such terminals is a trifle larger 

 than in the axone proper and stains a more intense red. It is already known that the 



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