vii STRUCTURE AND ORGANISATION OF NERVE 47 



various observations on its origin from the corresponding cells, 

 made by M. Schultze on the large nerve-cells of the spinal cord 

 and brain in vertebrates, and by Hans Schulze with even greater 

 success on invertebrates. In both cases the bodies of the 

 ganglion -cells also showed a more or less definite fibrillated 

 structure, which was most obvious in the cortex. This was the 

 more easy to recognise since adjacent fibrils were separated by 

 comparatively thick layers of plasmatic ground-substance. The 

 complicated course of the single small fibres within the cell 

 appeared, according to M. Schultze, with special clearness in 

 certain conspicuous multipolar ganglion-cells in the brain of the 

 torpedo, where it is easy to recognise that the fibrils partly 

 radiate in different directions from each process into the body 

 of the cell, and partly describe concentric circles round the 

 central nucleus. Any doubt as to the pre- existence of a 

 fibrillated structure of the axis-cylinder was finally removed by 

 the investigation of the broad non-medullated nerve-fibres of 

 Petromyzon, which are even better adapted than certain fibres 

 of invertebrates (e.g. crayfish) to demonstrate these structural 

 relations in the living preparation (Schiefferdecker, 7). Within 

 the sheath of Schwann two substances may usually be recognised : 

 (a) a bundle of the finest fibres situated in the axis (nerve-fibrils, 

 axis-fibrils), which often exhibit an undulating course, and are 

 closely invested with (&) a homogeneous substance, which no 

 doubt penetrates into the interior of the " axial filament," as 

 Schiefferdecker named the bundle of fibrils and there separates 

 the single fibrils, some 0'4 ^ thick (Fig. 152). There is .between 

 the latter and the homogeneous ground - substance (Kolliker's 

 neuroplasm, " axoplasma ") a similar relation to that in smooth 

 and striated muscle-fibres between contractile fibrils and sarco- 

 plasm. The layer of axoplasm is best developed in the thickest 

 nerve-fibres, and forms a smaller constituent of the entire axis- 

 cylinder in proportion as the fibres are more slender. This is 

 plainly seen in transverse sections of hardened nerve-fibres (Fig. 

 156). The central bundle of fibrils seems to be almost equally 

 developed in large and in small fibres, while the extent of the 

 axoplasma varies considerably. " With decreasing diameter of 

 axis-cylinder, the mass of axoplasm diminishes more rapidly in 

 Petromyzon than the number of fibrils. Since these last are 

 probably the true conducting substance, it is impossible in 



