THE PACINIAN CORPUSCLES. 133 



stalk at one end. It is to be examined with a low 

 power to make sure that the fat is entirely removed ; 

 the debris may then be wiped away, a little fresh 

 serum added, a narrow slip of blotting-paper placed 

 close to the corpuscle to avert the pressure of the 

 cover-glass, which is then laid on and the specimen 

 examined. 



In these fresh preparations, owing to the extreme 

 transparency of the layers of the capsule, the core of 

 the corpuscle with the central fibre, together with 

 the mode of passage of the nerve fibre into this at 

 the stalk, can be made out better than after the 

 action of reagents. And still more so if the outer 

 layers of the capsule are removed altogether, as may 

 readily be done with fine needles under the dissect- 

 ing microscope, leaving only the core and the closely- 

 set layers of the capsule which immediately surround 

 it. In tearing away the outer layers it will often 

 happen that the perineural or neurilemmal sheath 

 which surrounds the nerve fibre as this passes into 

 the corpuscle is torn off along with them, since they 

 are directly continuous with it. 



These fresh preparations of the Pacinians are very 

 beautiful, but unfortunately they cannot be preserved 

 in that state. Treatment with glycerine causes the 

 corpuscles to shrink and become too transparent, 

 and most of the ordinary staining fluids color the 

 core too deeply and obscure the termination of the 

 nerve fibre. If it he desired to preserve any such 

 preparation as showing some one or more points 

 particularly well, the cautious employment of osmic 

 acid prior to mounting in glycerine is most to be 

 recommended. The serum in which the corpuscle 

 is mounted must first be replaced by salt solution; 

 this again by 1 per cent, solution of osmic acid, and 

 this after being left for an hour or more in contact 

 with the preparation by distilled water, whilst finally 

 a drop of glycerine is allowed gradually to diffuse 

 in from the edge of the cover-glass. 

 12 



