92 PHYSIOLOGY CHAP. 



Not a few other similar cases have been described by neuro- 

 pathologists ; but in the majority of them the loss of deep sensi- 

 bility was incomplete, or was associated with a slight disturbance 

 of superficial sensibility. 



In proof of the secondary importance of superficial sensibility 

 as compared with that of the muscles and the deep tissues in 

 general, we may refer to the experiment of Beaunis (1887) on the 

 function of the laryngeal muscles. After anaesthetising the 

 mucous membrane of the glottis of a tenor by the application 

 of cocaine, which also made it pale owing to vascular constric- 

 tion, he found that the intonation of the voice, that is, the exact 

 formation of the separate musical notes, was not appreciably 

 altered ; the purity and timbre of the sounds alone seemed some- 

 what affected, which might be due to the altered blood-supply of 

 the organ. The conclusion drawn by Beaunis seems satisfactory, 

 that " muscular sensibility plays the leading part in the tension 

 of the vocal cords by which accuracy of tone is determined, and 

 the sensibility of the mucous membrane only intervenes, if at all, 

 in a purely secondary manner." 



We have consequently sufficient evidence for assuming that 

 the muscular sensations which depend on specific sense organs 

 situated in the muscles, tendons, joints, and accessory organs of 

 the motor system are independent of the sensations of the skin 

 and adjacent mucous membrane. 



The founders of the theory of muscular sense as a sixth sense 

 were Charles Bell (1832) and Panizza (1834) (see Vol. III. p. 467). 

 They founded their entire theory on the phenomena of the dis- 

 organised movements of the limbs obtained after section of the 

 dorsal roots (root ataxy). 



E. H. Weber (1846) developed the theory of a sense by which 

 we become aware of the degree of muscular effort necessary to 

 overcome the resistance that opposes our movements, and gave 

 it the name of sense of effort (Kraftsinn). He succeeded by 

 ingenious experiments in demonstrating that we are able to 

 appreciate the difference between two weights far more exactly by 

 this sense than by tactile or pressure sensibility. By sensations 

 of pressure alone, such as those produced by weights upon the 

 fingers resting supinely upon a support, the difference in weights 

 which are as 29 : 30 can be perceived. When the muscle sense is 

 employed, as in raising with the fingers a pan on which the 

 weights are placed, we are able to distinguish them when the 

 values are in the ratio of 39 : 40. In this case (according to 

 Weber) the lower threshold of difference does not depend on the 

 association of tactile and muscular sensations, because in judging 

 of the weights raised we entirely neglect the sensation of pressure 

 of which we are aware in the hand that supports the scale-pan. 

 In fact our judgment does not alter when we voluntarily increase 



