GENERAL SENSATIONS. 547 



recognized when the entire surface of the body is exposed to 

 them. The foregoing facts are well known to persons in the 

 habit of testing the temperature of a warm bath without the aid 

 of a thermometer ; they do not use the limited surface of a sen- 

 sitive tactile finger tip, but plunge the entire arm into the water. 

 The elbow, indeed, is the common test used by nurses in ascer- 

 taining that the water in which they are about to wash an infant 

 is not too warm for that purpose. 



Great extremes of heat or cold, such, in fact, as would act as 

 stimuli to a nerve fibre, do not give rise to sensations of different 

 temperatures, but simply excite feelings of pain. Thus, if one 

 plunges one's hand into a freezing mixture or into extremely hot 

 water, it is difficult to say at once whether they are hot or cold 

 in both cases pain being the only sensation produced. 



GENERAL SENSATIONS. 



We call general sensations those feelings, pleasurable or other- 

 wise, which can be excited in us, without our being able to refer 

 them to external objects, or compare their sensation with those 

 of the special senses, or even to describe their exact mode of 

 perception. Under this head are enumerated Pain, Hunger, 

 Thirst, Nausea, Giddiness, Shivering, Titillation, Fatigue, etc. 



Of these, only pain is commonly referred to any given part, 

 and the attempt to localize pain with exactness soon shows how 

 very different is our power in this respect in the case of pain and 

 in the case of tactile impressions. Thus, when we strike our 

 " funny bone" (the ulnar nerve passing over the condyle of the 

 humerus), by the tactile impressions of the skin we know the 

 elbow is the injured part, but the locality of the pain is not so 

 exactly to be determined, for it shoots down the arm to the little 

 finger, and is indefinitely spread over the region to which the 

 nerve is distributed. 



In studying the laws which govern the perception of painful 

 impressions, we must make the experiments upon ourselves, since 

 we alone can form conclusions from the sensations produced. 



The best way to carry out experiments upon pain is to use ex- 

 tremes of temperature, as we can thus graduate the stimulation. 



