174 THE HUMAN BODY 



Muscular feelings are, as already pointed out, frequently and 

 closely combined not only with visual but also with tactile, in pro- 

 viding sensations on which to base judgments: 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 com- 

 bining the tactile feelings it gives rise to, with the muscular feelings 

 accompanying 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 inter- 

 pret, 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 measure- 

 ment, 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 contact with the thing looked at. 



When we wish to estimate the weight of an object we always, 

 when possible, lift it, and so combine muscular with tactile sensa- 

 tions. By this means we can form much better judgments. While 

 with touch alone just perceptibly different pressures have the 

 ratio 1 : 3, with the muscular sense added differences of 7 can be 

 perceived. 



Hunger and Thirst. These sensations, which regulate the taking 

 of food, are peripherally localized in consciousness, the former in 

 the stomach and the latter in the throat, and local conditions no 

 doubt play a part in their production; though general states of the 

 Body are also concerned. 



Hunger in its first stages may be due to a condition of the gastric 

 mucous membrane which comes on when the stomach is empty, 

 since it is temporarily stilled by filling the organ with indigestible 

 substances. But soon the feeling comes back intensified and can 

 only be allayed by the ingestion of nutritive substances; provided 

 these are absorbed and reach the blood, their mode of entry is un- 

 essential; the hunger may be stayed by injections of food into the 

 rectum as well as by putting it into the stomach. 



Similarly, thirst may be temporarily relieved by moistening the 

 throat without swallowing, but then soon returns; while it may be 

 permanently relieved by water injections into the veins, without 

 wetting the throat. 



While both sensations depend in part on local peripheral con- 



