XXXIV.] NERVES OF SKIN. 377 



splits up into fine fibrils, which penetrate into the epithelial layer 

 and run between the epithelial cells, and sometimes anastomose 

 with each other, to end in free points which do not form connec- 

 tions with any structure in the epidermis. In the skin these 

 fibrils are confined to the rete Malpighii, and do not reach the 

 stratum granulosum. 



I. V.S. Skin (gold). Use boiled gold chloride and formic acid 

 (p. 372). Take very small pieces (2 mm. cubes) of the palmar 

 skin of the fingers or toes, preferably from a new-born child or a 

 young infant; cut away all the adipose tissue, and place the pieces 

 in the gold mixture for at least one hour. Then place the tissue in 

 slightly acidulated water, and expose to sunlight until the gold is 

 reduced. Harden in alcohol, and mount the sections in formic 

 glycerine. 



(H) Observe the blackened fine nerve-fibrils. Some of them 

 beaded, running between the epithelial cells (fig. 336). 



II. Terminal Corpuscles. They are very varied in their form, 

 and include the following : 



A. Simple tactile cells. 



B. Compound tactile cells. 



C. End-bulbs with many modifications. 



D. Touch-corpuscles. 



A. Simple Tactile Cells V.S. Skin (gold) (H). Treat very 

 small pieces of the human skin 



(volar surface of finger or toe) 

 or the snout of a pig by the 

 boiled gold formic acid method. 

 (a.) Observe a nerve-fibre 

 ((ig. 346, n) passing towards 

 and entering the epidermis, 

 where it is non-medullated and 

 splits into fibrils, which ter- 

 minate in oval, nucleated, tactile 

 discs or menisci (m), each of 

 which lies under a tactile cell 

 (a). The cells are 6-12 /x in 



length, and lie in the deeper FIG. ^.-Tactile Cells Snout of Pig . Xcrve- 



. , . fibre ; a. Tactile cell ; m. Tactile disc. 



part of the epidermis. 



B. Compound Tactile Cells, called also Grandry's and Merkcl's 

 Corpuscles, consist of two or more cells (15 p. x 50 //.) piled one on 

 the other ; between each two cells is a disc or plate tactile disc 

 which is connected with the axis-cylinder of a nerve. The cells 

 have a large pale nucleus, and the whole is surrounded by a fibrous 

 capsule. The nerve loses its myelin after it passes into the organ, 



