704 TASTE AND SMELL. [CH. LII. 



intact ; in this way the muscular sense may be destroyed without 

 the tactile sense being much affected. 



Those who believe in the muscular sense are again divided 

 into two sets ; some believe that the muscular sense is an accom- 

 paniment of the efferent impulse and it is variously spoken of as 

 an estimation of will force, or a sense of expended energy ; others, 

 and among these the majority of physiologists must be included, 

 look upon the sense as due to efferent impulses from the muscles 

 to the brain. The " estimation of will force " doctrine is put out 

 of court by the fact that people know when their muscles are 

 contracting, and whether they are contracting much or little, 

 when there is no expenditure of will force at all, as when the 

 muscles are made to contract artificially under the influence cf 

 electrical stimulation. There are now many anatomical facts 

 which point to the correctness of the view that the muscular 

 sense is a true sense. Many years ago it was shown that out 

 of the nerve-fibres which go to the frog's sartorius some few- 

 degenerate after section of the posterior nerve-roots. This has 

 been more recently demonstrated to be also the case in the muscles 

 of mammals by Sherrington. The discovery of sensory nerve- 

 endings in muscle and tendon points in the same direction. 



CHAPTER LII. 



TASTE AND SMELL. 



THESE two senses are very closely allied to one another, and it 

 will therefore be convenient to consider them in one chapter. 



Taste. 



Certain anatomical facts must be studied first in connection 

 with the tongue, the upper surface of which is concerned in the 

 reception of taste stimuli. 



The tongue is a muscular organ covered by mucous membrane. 

 The muscles, which form the greater part of the substance of 

 the tongue (intrinsic muscles) are termed linguales ; and by 

 these, which arc attached to the mucous membrane, its smaller 

 and more delicate movements are performed. 



