546 MANUAL OF PHYSIOLOGY. 



"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. 

 The application of a liquid over 50 C., or below 2 C., causes 

 pain. The suddenness of application to the part, and its dura- 

 tion, and the extent of surface, as well as the previous tempera- 

 ture, have important influence in the amount of pain produced. 



The various kinds of pain which we are all more or less 

 familiar with seem to be related in some way to their mode of 

 production, but we are unable to assign any definite cause for 

 these differences of character. Thus, though such terms as shoot- 

 ing, stabbing, burning, throbbing, boring, racking, dragging 

 pain, have a tolerably clear meaning in general, and may be of 

 diagnostic value, we have only an indistinct knowledge that 

 throbbing depends on excessive vascular distension in a part, that 

 sharp pains are produced by sudden excitation of a sensitive part, 

 and the dull pains by the more permanent stimulation of a part 

 less well supplied with nerves. 



Further, pain as we think of it is a complex mental process, 

 made up of many items, such as real sensory impressions, fear, 

 disgust, etc. When a finger is being lanced patients often cry 

 out most loudly before they are touched with the knife, and show 

 intense feeling when they look at the blood flowing from the 

 wound. 



Hunger and thirst are peculiar and indefinite sensations which 

 are experienced when some time has elapsed since food or drink 

 has been taken. The exact part of the nervous system in which 

 these impressions arise has not been determined. They are, how- 

 ever, said to be associated with peculiar sensations in the stomach 



