Herrick-Coghill, Nave Endings in the Skin. 39 



Inasmuch as the epithehal layers of the mouth and tongue 

 are morphologically only portions of the skin, it is necessary to ex- 

 amine these regions for light on the nerve endings as they may 

 be modified under the special conditions here existing. In the 

 frog, which has been the subject of the most elaborate invstiga- 

 tion, the sense of taste cannot be at all highly developed, for 

 the animal is accustomed to swallow its food, chiefly 

 horny coated insects, without mastication ; and experiments 

 (Bethe) prove a very sluggish response to chemical irritants. In 

 the tongue of the frog, as well as in the palate, there are num- 

 erous scattered specific sense organs, those of the tongue being 

 flat end-plates, while those of the palate are protuberant sensory 

 papillae. Athough these organs were described by Leydig in 

 1858 they have frequently been the objects of special study 

 since then and even now authors are not wholly in agreement as 

 to the details of the structure. The cellular elements in these 

 sense organs consist of the cylinder of flask cells forming the 

 protection for the sensory rod cells, a subordinate variety of 

 which has been termed forked cells by reason of the divided 

 peripheral projection. Alate, or winged cells, around the cup 

 or flask have also been noticed by some authors. Bethe, who 

 has recently studied these buds by means of the modification of 

 the methylene blue method which bears his name, finds two 

 sorts of nervous termini in them : first, free termini lying be- 

 tween the cylinder cells and reaching the surface, second ter- 

 mini with bulb-like expansions on various cells. (Fig. 8.) One 

 type of such endings is three-lobed and such endings are affixed 

 to the sides of the cylinder cells ; the other variety has simple 

 circular end-plates and these endings are found on the rod cells, 

 fork-cells and possibly also on cylinder cells. In no case did 

 Bethe succeed in finding actual continuity between the rod-cells 

 and the nerve. He in fact seems to find greater intimacy of 

 connection between the cylinder cells, which are not supposed 

 to have a nervous function, than with the rod-cells and in no 

 case is there more than a contact with the cell wall. He explains 

 the continuity detected by Arnstein and others as the result of 

 faulty observation and imperfect methods. In the ordinary pave- 

 ment epithelium of the palate Bethe finds termini on gland cells 

 and ciliated cells, as well as deeper elements. It should be 

 noted that the finding of the three-lobed end-plates on the cy- 

 linder cells was not a uniform occurrence but rather exceptional 

 and the suggestion is near that this is the result of an accidental 

 state of the fibers and not a natural or permanent organ. 



