TISSUES OF THE BODY. 



309 



an elongated oval or fusiform nucleus may be remarked, measuring about 

 0'0068-0'0113 mm. in length. At times, also, these flat fibres are split 

 up, though imperfectly, into fibrillrc (fig. 299, b). 



As to the nature of these fibres of Remak, whether they are composed 

 of connective-tissue, or are (as was supposed by their discoverer, and with 

 him by J. Mullcr) nervous elements, are points which, in the annals of 

 histology, have been the subjects of controversy for years past. The 

 existence of similar pale nerve elements among the lower animals and in 

 the petromyzon, and among the embryonic and olfactory fibres of the 

 higher animals, seems to point to the conclusion that they are of nervous 

 nature, and, indeed, the general opinion grows stronger from year to year 

 that this is the case. They are just nerve-fibres destitute of medullary 

 sheath, and in which the axis cylinder is enclosed within a nucleated 



Fig. 299. Remaps fibres from the calf 

 a, simple flat nucleated bands; 6, a 

 fibre split above into fibrilL*. 



Fig. ^00. A small nervous 

 branch from the sympathetic 

 of a mammal. Two dark- 

 bordered nerve tubes, a, 

 among a number of Remak's 

 fibres, 6. 



neurilemma. On the other hand, it must be granted that young imma- 

 ture connective-tissue may present precisely the same appearance. The 

 nucleated envelope of many ganglion cells is also a difficult point for ns, 

 which will be discussed in the next chapter. 



In some small trunks of the sympathetic system (fig. 300), the propor- 

 tion of these pale fibres (/;) is so large, and the number of the medullated 

 tubes is so small, that it is difficult to conceive what would be the object 

 of such an enormous amount of enveloping connective-tissue for so few 

 nervous fibres. 



In the nerves of the spleen of fully developed mammals twigs have been 

 found of 0'45 mm. in thickness, which contain nothing but Remains fibres. 



The question whether this variety in the appearance of the nerve-fibres 

 corresponds to a difference in their functions ox energies must be generally 

 negatived. The nerves of voluntary muscle and those of the skin have, 

 for instance, the same kind of fibres. The preponderance, however, of 

 narrow dark tubes in the sympathetic is certainly remarkable, but the 

 same occur in great abundance in the brain and spinal cord. Transitions 

 from broad to narrow fibres are also numerous, and in the sympathetic 



