IS2 



PHYSIOLOGY 



CHAP. 



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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 



FIG. 130. -Section of epidermis from skin of finger, substance (eleidiu) that 

 coloured by picro-carmme. (Ranvier.) a, stratum . N ' 



corneum; b, stratum lueidum, with scales of eleidin; staiUS deeply With 

 c, stratum granulosum full of eleidin granules ;<?,/, i 



deep cells and intercellular canals of rete mucosum ; ^Stratum granillOSUm 



c. dentations of deepest cells, for attachment to T onrravTinncA 



cutis vera. J^dnge liailSj. 



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 

 lueidum 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 



! 1 1 ll u- FIG. 131. Skin of the negro, \ertical 



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 a 



section, 250 diameters. (Kiilliker.) 

 o, a, cutaneous papillae ; 1>, undermost 

 and dark - coloured layer of vertical 

 epidermis cells ; c, mucous or Malpi- 

 ghian layer ; (/, horny layer. 



