348 SPECIAL PHYSIOLOGY. 



sensation of resistance within the joints, is also very evident. The in- 

 ternal sensations proper to the states of the nervous system, or the 

 nervous internal sensations, are those of pain generally, especially of 

 neuralgic pains, sensations of vertigo, torpor, drowsiness, mental fatigue, 

 nervous exhaustion or shock, and irresistible tendency to sleep. 

 . The muscular sensations are those of uncomfortableness, restless- 

 ness, muscular languor, faintness, lassitude, heaviness, fatigue, weari- 

 ness, as shown in the heavy falling eyelids and bodily exhaustion 

 which precede sleep, intermittent spasm and cramp, and the feelings 

 of general health, buoyancy, bodily energy, arid capacity for corpo- 

 real work. It is also by a similar class of sensations, which, less 

 vague in their seat, are known under the collective name of the mus- 

 cular sense, that we become conscious of the degree of effort made, or 

 of the resistance met with and overcome, in regulating the amount of 

 force employed in all the muscular movements of the body, such as 

 lifting or moving weights, resisting external forces, balancing the 

 body in walking, moving the arms in the performance of prehensile 

 and manipulative acts, and exercising the organs of voice and speech. 

 When this sense is lost in certain muscles, their actions can no longer 

 be regulated, or even commanded, except through the agency of the 

 sight (page 287). On board a ship in a rolling sea, the muscular sense 

 is called into unusual activity to neutralize the effect of the motions of 

 the vessel, which disturb the equilibrium of the body; on returning 

 to land, the compensatory movements rendered necessary at sea, con- 

 tinue for a time. 



To this sense, moreover, we owe our feeling of the stability of posi- 

 tion of the body, in sitting or in standing ; when it is wanting, vertigo 

 or giddiness ensues, caused by a loss of the sense of equilibrium, and 

 accompanied by staggering efforts at recovery of position, or by fall- 

 ing. Vertigo may be produced by rapid rotatory movements of the 

 body, whether active or passive ; also by the long maintenance of the 

 horizontal posture, by various diseases, by injuries of the head, and by 

 many medicinal agents. Though manifested by, and referred to, mus- 

 cular actions, its real cause is some disturbance in the nervous centres, 

 which govern and co-ordinate these movements. 



Our notions of space and distance, are also derived, or deduced as 

 inferences, from the exercise of the muscular sense, which enables us 

 to determine the precise position of the body, when at rest, or in 

 motion through space. The relative positions of external bodies, 

 whether these be at rest or in motion, are also determined by refer- 

 ence to the fixed or movable state of our own bodies. If we are at 

 rest, moving objects appear to us to move, and stationary ones to be 

 fixed. But if, being at rest, we imagine ourselves, through a dis- 

 turbance of the muscular sense, to be in motion, or if we perform ir- 

 regular and erroneously estimated movements, then external objects 

 seem to move accordingly; on the contrary, the movements of out- 

 ward objects may, after a time, seem to depend on motion in our own 

 bodies. In the former case, we refer a bodily condition of movement 

 to the outer world ; in the latter, movements in the outer world are 

 referred to a supposed bodily condition. In this latter case, giddiness 



