566 THE HUMAN BODY. 



As, however, we can determine more accurately the differ- 

 ence between two weights when we lift them than we can 

 when they are merely laid on a hand supported by a table 

 (see below), there are undoubtedly (apart from cramp and 

 fatigue) true muscular sensations distinct from tactile; and 

 that these, or some of them, are central in origin seems 

 proved by certain phenomena observed in disease. Persons 

 suffering from paresis, i.e. muscular weakness not amount- 

 ing to complete paralysis, make (until they have learned to 

 interpret correctly their sensations under the new condi- 

 tions) entirely wrong judgments as to the extent of their 

 movements; they think they have contracted their muscles 

 much more than is really the case. If the muscular sense 

 depended on stimulation of sensory nerves in the mus- 

 cles this error could not arise, for the intensity of the sen- 

 sation would be determined by the amount of contraction 

 which actually occurred. 



We have already seen how closely muscular sensations 

 are combined with visual in enabling us to form judgments 

 as to the distance, size, and movements of objects. They 

 are as closely combined in ordinary life with tactile sensa- 

 tions; in the dark, when an object is of such size and form 

 that it cannot be felt all over by any one region of the skin, 

 we deduce its shape and extent by combining the tactile 

 feelings it gives rise to, with the muscular feelings accom- 

 panying the movements of the hands over it. Even when the 

 eyes are used the sensations attained through them mainly 

 serve as short-cuts which we have learned by experience to 

 interpret, as telling us what tactile and muscular feelings the 

 object seen would give us if felt; and, in regard to distant 

 points, although we have learnt to apply arbitrarily selected 

 standards of neasurement, it is probable that distance, in 

 relation to perception, is primarily a judgment as to how 

 much muscular effort would be needed to come into con- 

 tact with the thing looked at. 



When we wish to estimate accurately the weight of an 

 object we always, when possible, lift it, and so combine mus- 

 cular with tactile sensations. By this means we can form 

 much better judgments. While with touch alone just percep- 



