THE NERYOl'S SYSTEM. 



391 



or whitish and pearly, and it is obviously to it that the 

 peculiar glistening appearance of the nerves is due. The nerve- 

 pulp, is rapidly and invariably altered by the application of 

 cold water, of most acids, and of many other reagents, the change 

 consisting principally in a coagulation of it, which takes place 

 gradually from without to within, sometimes involving the entire 

 thickness, sometimes only its outermost layer. In the latter 

 case, are produced the well-known nerve-fibres with double 

 contour lines (fig. 137, 2, 3, 4), or in which the medullary 

 sheath is, externally, coagulated to a greater or less extent, 

 remaining fluid internally ; in the former case, with the con- 

 tents apparently wholly grumous and opaque (fig. 138). The 



coagulated nerve-medulla, in „. ,„_ 



° ' rig. 138. 



fact, seldom appears homoge- 

 neous, but most generally 

 grumous, granular, and as if 

 composed of separate, irre- 

 gular, larger and smaller 

 masses, and, upon the ap- 

 plication of acetic acid, as 

 if formed of minute, separate, 

 or reticularly united rods. 

 The nerve-pulp is also al- 

 tered very readily by pres- 

 sure. It sometimes escapes g*p 

 from the ends of the tubes, 

 or from hernial protrusions 

 or ruptures of the sheath, 

 forming larger or smaller drops of every imaginable shape, 

 regularly spherical, clavate, fusiform, cylindrical, filamentary, 

 or of the most bizarre figures, wdiich likewise coagulate either 

 on the surface merely, or throughout, and thence, like the 

 nerves, appear with a double contour, or half or wholly grumous. 

 But, within the fibres also, its structural conditions alter, for, in- 

 stead of being continued through them as before, — as a cylinder 

 of uniform size, — it accumulates in places into larger masses. In 

 this way are produced the frequently described, varicose nerve- 



Fig. 138. Nerve-tubes of Man, x ."00 diam.: four fine, two of which arc varicose; 

 one of medium size with simple contours ; and four thick, two of which have double 

 contours, and two, grumous contents. 



