284 THE NERVOUS SYSTEM 



There are the Pacinian corpuscles, Meissner's corpuscles, 

 the encl-bulbs, the nerve-plexus surrounding the hairs, and 

 the free nerve-endings which ramify in the epitheUum. 

 Attempts have been made to identify each of these with 

 some particular sensation. It is beUeved by some authorities 

 that the corpuscles of Pacini and of Meissner are receptive 

 to touch and the end-bulbs to temperature. It is natural 

 to regard the nerve-plexus of the hairs as sensitive to 

 touch. Pain is commonly held to be evoked by the free 

 nerve-endings, the chief ground for this belief being that 

 the cornea, in which these are the only nerve-endings 

 present, is sensitive only to pain. 



Deep sensation. — When an object is pressed against the 

 skin with sufficient force to cause deformation of the skin, 

 there is set up a complex of sensations, arising partly 

 from the skin and partly from the deep structures, such 

 as the muscles and their tendons. Our estimation of the 

 texture, hardness and shape of objects is derived from an 

 analysis of the combination of superficial and deep 

 sensations. 



Head, partly as the result of an experiment performed 

 upon himself, showed that after section of a cutaneous 

 sensory nerve recovery took place in two well-marked 

 stages. In the first stage, which is usually fully estab- 

 Mshed six months after section, pain of a burning, dis- 

 agreeable character is felt, touch feels rough, and there 

 is a crude form of temperature sense. Heat is only felt 

 when above 38° C, and cold only when below 24° C. All 

 the sensations are poorly localised and tend to radiate 

 widely. This form of sensation Head terms protopathic. 



In the second stage pain becomes more bearable and 

 more definitely locahsed, the sense of touch becomes more 

 delicate, while fine grades of temperature are appreciated. 

 This form of sensation is known as epicritic. Deep sensi- 

 bility, in which two elements are recognised, deep pressure 

 and pressure pain, is not lost unless the motor nerves are 



