SENSATIONS AND THE SENSE-ORGANS 141 



their receptors than to those produced by the abnormal 

 method. 



A closely related experience is that of the victim of 

 an amputation. He describes minutely pains and other 

 feelings which seem to come from the lost limb. We 

 have only to reflect that all the fibers which formerly 

 conducted impulses from the missing part are still 

 present in the stump and if they are stimulated by 

 reason of temporary conditions there they will give rise 

 to the old, familiar sensations. The engineer of a steam- 

 boat cannot tell whether his gong has been rung from 

 the pilot house or from some other station. We are 

 usually saved from confusion by an important property 

 of the afferent system: that nerve fibers are much more 

 resistant to stimulation along their course than at their 

 specialized receptive terminations. 



The Classification of Sensations. The five senses 

 ordinarily recognized do not satisfy the requirements of 

 an inclusive enumeration. They are all of the class 

 which the physiologist calls special. He sets over against 

 them another group, the common or general sensations, 

 in which he places those which seem to have their 

 causation within the body. Special sensations are 

 those referred to the external world. Examples of 

 common sensations are hunger, thirst, fatigue, nausea, 

 and many kinds of pain. One is struck with the 

 prominence of disagreeable feelings in this class and 

 this may be connected with the fact that they usually 

 stand for conditions that call for readjustment. Be- 

 cause these sensations are unpleasant we are prompted 

 to take measures for their abatement and the interest 

 of the organism is served. 



There are some sensations which lie on the border 

 line between the general and the special orders. In 

 explaining how the equilibrium is preserved we men- 

 tioned the afferent impulses from the musculature. 

 These are mostly applied subconsciously to produce 

 appropriate reflexes but this is not the whole story. 



