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VETERINARY PHYSIOLOGY 



Much of our knowledge 

 cutaneous mechanisms has 



— b 



Fig. 43. — Simple form of sensory 

 nerve termination. In the tac- 

 tile corpuscle the nerve fibre 

 coils round the capsule before 

 entering. (Dogiel. ) 



nocuous or painful stimuli 

 seem to be independent. 



of the mode of action of these 

 been gained by a study of the 

 relation of the changes of con- 

 sciousness to the nature of the 

 stimuli producing them. 



In studying reflex action 

 it has been seen that the 

 stimuli acting upon the skin 

 may be divided into harmful, 

 or nocuous, and non-harmful, 

 and that these tend to produce 

 different reactions and are 

 accompanied by different kinds 

 of sensation — the former char- 

 acterised as unpleasant or pain- 

 ful; the latter by othercharacters, 

 such as contact, warmth, or cold. 

 The mechanisms for the 

 reception and transmission of 



and of ordinary cutaneous stimuli 



1. Reaction to Nocuous Stimuli— Pain. 



By exploring the surface of any small area of skin with 

 the point of a very sharp needle it will be found that prick- 

 ing certain parts gives rise to a more painful sensation than 

 pricking other parts. The first may be called pain spots. 

 By gentle pressure by a bristle with a rounded end other 

 spots may be discovered, which, when touched, give a 

 sensation of contact. These are the touch spots. Pieces of 

 skin cut out from the pain spots show no special nerve end- 

 ings, but pieces cut out from the touch spots show the 

 presence of a tactile corpuscle in a papilla under the 

 epidermis. 



It must be recognised that the mechanism of the pain 

 spots has been developed to lead to appropriate responses to 

 nocuous stimuli, and that the implication of consciousness 

 is secondary. 



