88 PHYSIOLOGY CHAP. 



such as occur in other special regions of the skin and other 

 mucous membranes. But this association is neither constant nor 

 necessary, and probably depends on the summation of particular 

 conditions of excitability in the sensory centres. 



VI. In the group of functional sensations, that is the sensa- 

 tions that accompany the various functions of the internal organs, 

 a peculiar importance, both from the physiological and from the 

 psychological point of view, attaches to the sensations by which we 

 become aware, directly or indirectly, of the state of the muscles, 

 the modes and different degrees of their functional activity, and 

 the changes, generally speaking, in the active and passive organs 

 of the motor system. It is by the sum of the sensations arising 

 from the motor system that we are able to control our movements, 

 and to carry them out with the necessary precision. 



The character of these sensations is always vague and ill- 

 defined. The slight degree of tension normally present in inactive 

 muscle, on which muscular tone depends, certainly lies below the 

 threshold of consciousness. We are able without hesitation to 

 call up the exact degree of muscular contraction necessary to 

 reach a given aim, e.g. to produce a musical note of a certain 

 pitch. This means that we have, unconsciously, an exact notion 

 of the degree of tension present in the vocal muscles previous to 

 their voluntary contraction. 



The sensations of tension and resistance that accompany the 

 state of contraction and the contractile movement of the muscles 

 are obscurely perceived. 



With the eyes blindfolded or in total darkness, we are 

 conscious of a certain position in which we place, say, an arm ; 

 we are able to describe it, and even to imitate and reproduce it 

 exactly with the other arm. We are aware of the changes of 

 movement of the arm, whether these are made voluntarily or 

 passively. 



When we lift a weight, or in an active movement meet with 

 an obstacle or a resistance imposed by a body external to the 

 limb, we are able to apprehend the degree of effort exerted in 

 raising the object or removing it. The estimation we make of 

 our sensations of tension and resistance, and of the force required 

 to overcome them, are, as we shall see, the most important elements 

 in the judgment we form of the weight of objects. 



These and other more obscure, less well defined, and poorly 

 localised bodily sensations which accompany functional activity 

 of the motor organs in animal life are collected by the majority of 

 physiologists into one category known as the muscular sensations. 



This term is inappropriate, and must be rejected as erroneous 

 if it is taken to mean that all the different varieties of sensations 

 which it comprises originate from specific sensory elements con- 

 tained in the muscles ; for we reason experimentally that most of 



