482 



PHYSIOLOGY 



CHAP. 



fc.1... ... > 



FKI. 130. Section of epidermis from skin of finger, 

 coloured by picro-carmine. (Ranvier.) a, stratum 

 corneum ; 6, stratum lucidum, with scales of eleidin ; 

 c, stratum granulosum full of eleidin granules ; d, 

 deep cells and intercellular canals of rete mucosum ; 

 e, dentations of deepest cells, for attachment to 

 cutis vera. 



Between the connecting bridges there is a system of intercellular 



channels (Bizzozero) which may become dilated with excess of 



fluid, on which the bridges 

 between the cells are more 

 apparent. These spiny cells 

 contain pigment granules, 

 which are more abundant 

 in proportion as the skin is 

 darker. The colour of the 

 skin in the black races is 

 due to this pigment, which 

 is particularly plentiful in 

 the deeper cells of the Mal- 

 pighian layer (Fig. 131). 



The more superficial cells 

 of this layer are spindle- 

 shaped, and contain a 

 number of granules of a 

 substance (eleidiu) that 

 stains deeply with carmine 

 (stratum granulosum of 

 Langerhans). 



Between this and the 



horny superficial stratum there is in some parts of the skin an 



intermediate layer which looks clear, 



and is formed of cells with indistinct 



outlines ; this is probably a transition 



between the cells of the granular and 



those of the horny layers (stratum 



lucidum of Oehl). 



The cells of the stratum corneum, 



which are nearly all destitute of a 



nucleus, may be regarded as senile 



cells, degenerated into horny sub- 

 stance, which, in proportion as they 



approach the surface, lose all their 



vital character and are finally reduced 



to hard, dry, transparent scales, 



perpetually cast off from the surface 



of the skin by desquamation (scurf). 



So that by this continual shedding 



of the superficial lamellae, which 



are replaced by those of the sub- 

 jacent layers, the body suffers a 



constant loss of horny substance, 



comparable with any other loss of substance by excretion. 



The horny scales give no protein reaction, but contain 



Fin. 131. Skin of the ne^ro. Vt'Hirnl 

 section, 250 diameters. (Kiilliker.) 

 a, a, cutaneous papillae ; ?), undermost 

 and dark - coloured layer of viTtii-il 

 epidermis cells ; c, mucous or Malpi- 

 ghian layer ; d, horny layer. 



