Connective Tissue, Nerve, and Muscle. 523 



used for establishing the individual characters of elastic tissue have been 

 instrumental in producing erroneous notions as to its origin. 



Thus we have in skin, as in tendon, bundles of fibrillary tissue every- 

 where covered with flat cells, and, in the interstices of the bundles, the 

 analogues of the branched cells of the cornea, producing a ramifying net- 

 work of elastic tissue. 



In gold preparations of the skin, the blood-vessels and nerves can be 

 followed between the larger fasciculi, analogously to the position of the 

 nerves in the cornea. 



Fascia differs from skin and tendon only in so far as its flatness permits 

 and necessitates a change of form in the flat cells, and the easy study of 

 their arrangement and nature by nitrate of silver. If a half per cent, 

 solution is injected under the skin of a mouse's back and the animal killed 

 in from five to ten minutes afterwards, and the skin of the back dissected 

 off, the fascia which has been in contact with the silver is recognized by 

 its milky whiteness and oedematous condition. If spread out carefully 

 on the object-glass in glycerine and exposed to sunlight, it is seen to be 

 plated over with oblong or slightly rounded cells with large nuclei. 

 Figure 8, Plate IX., is a sketch from a part of a preparation so obtained. 

 The cells separated from the same structure by potash are represented 

 in figure 9, Plate IX. ; it will be observed that they are identical in 

 appearance. Figure 10, Plate IX., illustrates the very large flat cells, 

 with their nuclei, that cover the fascia of the muscles of the thigh of the 

 frog. 



Frequently, but not so constantly, the branched cells are also stained 

 by the silver, and they are generally found at a different focus. 



Ranvier ('Archives de Physiologic') has described flat cells on the 

 sheaths of nerve-fasciculi and the investing membrane of nerve-bundles 

 as constituting a lymphatic sheath. 



By means of the saturated potash solution I have been able to satisfy 

 myself that, not only are the nerve-bundles surrounded by lymphatic 

 sheaths, but that each medullated nerve-fibre is invested with a layer 

 of flat cells. This layer is closely applied to the medulla, and is 

 internal to the sheath of Schwann. It is composed of extremely fine 

 and delicate cells, and their demonstration by potash succeeds less fre- 

 quently than does that of the cornea-cells ; they are (as far as I have 

 seen) without exception long and narrow, often tapering to an exceedingly 

 fine point. In the finest forms their cellular nature is only to be distinctly 

 made out by a magnifying-power of 700 or 800 diameters. Figure 18, 

 Plate X., represents varieties of these cells and their relation to the 

 medulla. Their length varies from 0*075 to 0*036 millim. ; many of them 

 are not more than 0*0015 millim. broad. Appearances are sometimes seen 

 that would seem to indicate that the sheath of Schwann (tubular mem- 

 brane) is lined by a layer of flat cells, distinct from that covering the 

 medulla (white substance). The medulla, when treated by potash, presents 



