264 Proceedings of the Royal Irish Academy. 



cleaned off to right of mesial line. This may be due to some inter- 

 mingling of twigs of left trigeminus with twigs of right. Both being 

 present, there would not be so much recuperative power there as on 

 the left side, where only (the healthy) one present ; yet more than 

 on the right side, where the only one present was paralysed." 



The whiteness of the right half, comparing so strangely with the 

 redness of the left, continued for two or three days longer before the 

 tongue became completely clean. 



From these facts, it is imperative to conclude that the cleaning of 

 the tongue depends directly on the activity of the lingual branch of 

 the trigeminus. Where this activity was diminished, the region sup- 

 plied by the nerve remained loaded for a considerable time beyond the 

 period of the removal of the fur from the adjoining region, in which the 

 action of the nerve continued. This is a distinct revelation of the 

 trophic influence possessed by this trigeminal branch over the mucous 

 membrane, and papillae, to which its filaments are distributed. We 

 may infer from what precedes, that the pathological phenomenon of 

 furred tongue is due, at least in a great measure, to temporary paresis 

 of the lingual nerve. The fact that, in some cases, the fungiform 

 papillae stand out as red points over the white surface does not con- 

 tradict this opinion, but rather yields it support, inasmuch as their 

 nerve supply being greater than that given to the filiform papillae, 

 they would thus give way later. Conversely, it may be deduced from 

 the preceding facts, that where the tongue is abnormally red there is 

 unusual excitation of the nerve in question. 



Obviously, impairment of taste and touch is a necessary result of 

 the arrest of normal trophic change over the surface of the tongue. 

 When desquamation does not take place, or takes place but slowly, 

 the epithelial scales which remain interpose an obstacle to the due 

 conveyance of impressions ; and, whilst remaining, they may undergo 

 morbid change. The loaded tongue cannot perceive sapid impressions 

 well, and we have reason to presume a certain amount, or as it were 

 a film, of effete matter unremoved on the surface of the tongue, when- 

 ever there is paresis of the lingual nerve. Hence, we should be on 

 our guard against considering (as some have done) that the impair- 

 ment of taste which follows paralysis of this nerve is an absolute 

 demonstration of its gustatory power. 



An objection to my statement concerning nerve-influence in con- 

 nexion with the production of fur may, perhaps, be supposed to exist 

 in the opinion that the fur which appears on the tongue is formed by 

 external parasites. Some words on this subject are consequently 

 necessary. Whilst regarding this morbid phenomenon as due mainly 

 to the presence of altered or moulting epithelial cells, it is not, of 

 course, denied that minute plants may be found within the buccal 

 cavity. This has long been known ; and it may be added that they 

 appear not only on the tongue, but on the gums, and elsewhere, and 

 have not been regarded as essential to the formation of the fur, of 

 which Rindfleish, the distinguished histologist, remarks : — " What is 



