38 ELECTRO-PHYSIOLOGY CHAP. 



described Eemak's fibres as axis -cylinders with a sheatk of 

 Schwann, and they have since been very variously interpreted. 

 It was even questioned whether they were nerves at all, but 

 later on Schultze's opinion was very generally adopted. Eemak 

 observed that the fibres, which he described as naked, " and 

 nearly always longitudinally striated on the surface," were readily 

 decomposed into the " finest threads," and in fact nothing could 

 be easier than to demonstrate this in suitable, preparations, e.g. 

 the splenic nerves of ruminants. Kolliker and Schiefferdecker 

 (4), on the other hand, regarded each Eemak's fibre as " a bundle 

 of fine axis-cylinders, surrounded by a more or less complete sheath 

 of Schwann." The question again can only be determined by 

 reference to the origin of the fibres involved. If it can be shown 

 that a " Eemak's fibre " originates as a simple fibre, and that its 

 individual " elementary fibrils " are not independent cell processes, 

 there can then be no doubt that it represents a single axis- 

 cylinder (nerve-fibre), and not a bundle of such fibres. It has 

 long been known that broad prolongations spring from the sym- 

 pathetic ganglion-cells, which are invested with a complete sheath 

 of Schwann; and these, in their turn clothed with a process 

 of the cell sheath, correspond throughout with Eemak's fibres. 

 These last, in continuing their course (notwithstanding the in- 

 equalities of the cellular sheath as first remarked by Eanvier), 

 make good their existence as special structural elements, which 

 are easily isolated like the medullated nerve-fibres ; while the 

 elementary fibrils (" Eemak's fibrils," Kolliker) cling together much 

 more closely, and can only be isolated in places. It is, however, 

 easy to demonstrate their existence, both in teased preparations, 

 and at the cross-sections of large nerve-trunks containing Eemak's 

 fibres (splenic nerves of the ox). 



The elements of the olfactory nerve are similar in structure 

 to Eemak's fibres. As shown by M. Schultze, the peripheral 

 expansion of this nerve consists in all vertebrates of non-medullated 

 elements, which, e.g. in the pike, are clearly defined, and sur- 

 rounded by a tolerably thick structureless sheath, regarded by 

 Schultze as the sheath of Schwann. The single fibres, some 

 1040 fju in diameter, are round, or polygonal from pressure in 

 cross-section. The content of the sheath exhibits a somewhat 

 faint longitudinal striation even in the fresh state. After pro- 

 longed maceration in 0'04 / o chromic acid, or 0'4-0'6 % 



