214 THE SENSES OF ANIMALS 



has made us over-sensitive to pain. A toughening course 

 can teach almost anyone to be comfortable in surroundings 

 so hot or so cold that they would be highly distressing to a 

 person in soft condition — how many adults would care to 

 go out in winter weather with bare legs and ankle socks, as 

 so many children do without discomfort? It is the same with 

 pain, and one has only to watch a boxing match to realize 

 that the brain is able to ignore a great many messages from 

 the pain-receptors that would be interpreted as very painful 

 by an untrained person. In like manner no doubt the rough 

 and tumble of the life of a wild animal teaches it to ignore 

 the lesser painful stimuli and to attend only to those that 

 mean danger. In the cold-blooded animals, both vertebrate 

 and invertebrate, the sense of pain appears to be less acute, 

 for many of them are able to sustain injuries from which we 

 should die of shock, without reacting in a way that indicates 

 they are suffering severely. Their reactions show that they 

 do have a sense of pain, but the sensation is likely to be much 

 more transient than in higher animals and probably ceases 

 with the withdrawal of the stimulus. The matter of injury- 

 shock is, however, rather beyond our subject ; it is concerned 

 with other things, such as biochemistry and psychology, in 

 addition to the senses. 



The receptors for pain and for temperature both seem to 

 be of two kinds, those that are normally used for detailed 

 discrimination and those that respond to stronger stimuli. 

 The latter are known as the receptors of protopathic sensa- 

 tion; they need a very much stronger stimulus in order to 

 react, but once the sensation is aroused it is intense, long 

 lasting, and very distressing. The protopathic sensations are 

 those of very high or very low temperature and of great 

 pain. Everyone knows how acute, intense and long-lasting 

 the pain of a burnt finger can be long after the hand has 

 been snatched away from the stimulating flame; or how 

 excruciating it is when the fingers are dried and warmed 

 after they have been chilled by injudiciously joining in a 

 snowball game without gloves. The protopathic pain sensa- 

 tion is so crippling in its effects that some of the tricks of 

 unarmed combat are designed to produce it, whereas the 

 Queensberry Rules are designed to avoid it. 



