384 EXTERNAL INTEGUMENT. 



III. Nervous functions of the sJcin. 



The skin also possesses extremely varied functions, owing 

 to the numerous nerves terminating in it. We have already 

 studied the centrifugal nerves which innervate its smooth 

 muscles, and cause their contraction under reflex influence 

 (erection of the nipple, for instance), or which terminate in 

 the glands, and give rise to their secretion, this influence 

 appearing especially in the case of the sudoriferous glands. 



The skin, however, possesses the greatest number of cen- 

 tripetal or sensory nerves. These have, sometimes, general 

 functions which it is difficult to specify, such, for instance, as 

 their influence as centripetal organs and starting-points to 

 the respiratory reflex action (see' Respiration, p. 337). The 

 skin is, however, the chief seat of sensation. The epidermis 

 of all those parts of the skin which are extremely sensitive, 

 exhibit special features (papillae) connected with this sensi- 

 tiveness. Diseases of the epithelium have, therefore, a great 

 effect on the nervous system : we have already studied the 

 derangement produced by the chill which follows a too great 

 evaporation of sweat ; these derangements are, perhaps, often 

 only a nervous reaction, or reflex phenomenon, chiefly affecting 

 the vaso-motors of different organs ; pathology is more and 

 more tending to admit this, in order to explain what v> as 

 formerly dignified with the name of metastases (see p. 51).. 



The study of the sensory functions properly so called of 

 the skin, viz. feeling and touch, will serve better as an intro- 

 duction to that of the organs of the senses, propeny to 

 called. 



