THE PHYSICAL LAW OF MATTER 167 



can the medullary, or white, substance of Schwann, be 

 traced to ? and where can the substance of the axis 

 cylinder be evacuated ? An answer to these last two 

 questions seems to us to be almost impossible, but never- 

 theless, we think that the importance of the subject 

 demands that we should do our utmost to trace its 

 progress, until either failure, or success, follows. 



It is said that the white substance of Schwann ceases 

 to exist at a point some little distance from the nerve 

 terminals, and, if this be so, we must be prepared to 

 look for its elimination somewhere before the final 



FlG. 63. A, TWO TACTILE CELLS IN THE DEEPER PART OF THE HUMAN 

 EPIDERMIS. (Merkel.) B, ENDING OF NERVES IN TACTILE DISCS IN 



THE PIG'S SNOUT. (Ranvier.) 



n, nerve-fibre ; m, terminal menisci or tactile disks ; e, ordinary epithelium-cell ; 

 a, altered epithelium-cell, to which the meniscus is applied. 



distribution of these terminals. In doing so, however, 

 we fail to find any solution of continuity of its con- 

 taining membrane and, consequently, we must believe 

 that it finds its way out of its containing membrane at 

 the extremities of the nerve terminals, and so empties 

 them, that accounting for the above statement : this, we 



7 O * 



think, it does amid, and as, the epidermal cells, and 

 keratinous debris, forming the cuticular layers overlying 

 the true skin ; indeed, it might be said, without over- 



7 t Q / 



stretching the " scientific imagination," to lend itself to 

 the formation of these layers, and to be finally shed as 

 epidermal scales (Fig. 62), with the overlying and inter- 

 penetrating horny matrix of keratinous, and connecting, 

 or cementing, material. To this goal also may be traced 



