212 



NORMA L HISTOLO G Y. 



liberation of stored energy within the body, and causes it to appear 

 as heat. In conjunction with these functions the skin is also an 

 organ of tactile and thermal sensation, functions which are not 



Fig. 189. 



Hair-rudiment from an embryo of six weeks. (Kolliker.) a, horny layer of epidermis ; b, 

 Malpighian layer, rete mucosum ; i, limiting membrane; m, m, cells extending from the 

 rete mucosum to rill the future hair-follicles. The elongated cells near the base of the 

 sac are those from which hair is developed. The secreting glands of the body arise from 

 some epithelial layer in a similar manner. 



merely beneficial in themselves, but are useful auxiliaries in the 

 furthering of the other functions exercised by the skin. It is a 

 common experience that the sensation of cold stimulates the desire 



Fig. 190. 







Section of developing tooth. From embryo of sheep. (Bohm and Davidoff.) a, epi- 

 thelium of the gum; b, its deepest layer; c, superficial cells of the enamel-pulp; d, 

 enamel-pulp formed of modified epithelial cells ; s, cells of the enamel-pulp destined to 

 produce the enamel (" adamantoblasts"); p, dental papilla. 



for muscular exercise, of which the liberation of heat is a result. 

 The sensation of pain often gives timely warning of exposure to an 

 injury sufficiently great to overcome the usual protective powersof 



