vii STRUCTURE AND ORGANISATION OF NERVE 39 



solution of potassium chromate, Schultze succeeded in isolating 

 two kinds of elements from the nerve-fibres, i.e. countless minute 

 fibrils, and a finely-granulated mass, " of which it is hard to say 

 whether it forms part of the little fibres or lies between them." 

 This is the characteristic structure of the olfactory fibres ; and 

 here we have the first mention of a fibrillaUd structure of nerve- 

 fibre, which became the starting-point for the further investigations 

 by which Schultze established the doctrine of fibrillated structure 

 for all nerve-fibres. Eegarding the axis-cylinder of medullated 

 nerves as a bundle of the finest fibrils with granulated interfibrillar 

 substance, he compared it with the fibrous elements of the olfac- 

 tory nerves, and defined the latter as " axis-cylinders with a sheath 

 of Schwann." 



Babuchin objected to Schultze's theory, and declined to recog- 

 nise the sheathed " nerve-fibres " which Schultze isolated from the 

 olfactorius as comparable with the fibres of Eemak. Even if the 

 comparison is legitimate in many animals, it may be shown in other 

 cases that the supposed sheath of Schwann corresponds better 

 morphologically with the perineurium of the nerve-trunks. Fine 

 transverse sections of the olfactorius (of pike) show that secondary 

 septa run out from the external sheath of the large nerve " fibres " 

 (in Schultze's sense), and divide the fibre into two or more com- 

 partments. In the higher vertebrates, on the contrary, there is 

 no such marking out of single " fibres " by special sheaths. Boveri, 

 at any rate, has failed to find nucleated membranes, either by 

 isolation or in cross-section. " An arrangement of larger or 

 smaller irregular groups is indeed easily identified at the trans- 

 verse section, but they are not separated by sharp double lines, 

 as would be the case with membranes investing distinct parti- 

 tions. The dividing line is single, often obscure, and dotted in 

 appearance, in no way comparable with the secondary sheaths of 

 the pike's fibres." Boveri, therefore, assumes correctly that these 

 partition walls are " a superficial expansion of connective tissue, 

 such as are also found between the fibres of the white matter of 

 the spinal cord." This is borne out by the position of the nuclei. 

 " It is clear from the ' fibres ' of vertebrates higher than fishes that 

 the nuclei lie not only between but also inside them." 



The spaces within these septa are seen in cross-section to be 

 filled with a gray reticulum (the interfibrillar substance of Schultze), 

 in the meshes of which dotted sections of minute fibrils appear, 



