THE SKIN. 367 



epidermis ; if, however, the irritating influence be continued, 

 the malpighian layer itself resumes the embryonic globular 

 form, and by its proliferation gives rise to the formation 

 of pus. 



This deep and essentially living layer of the epidermis, 

 also gives rise to neoplasms of the tissue, or the different 

 forms of epithelial or cancroid cancers. In the malpighian 

 layer are found the pigment granules or corpuscles, which 

 shades the color of the skin in the colored races and in 

 some integuments (scrotum, the areola of the nipple, etc.). 

 This pigment of the rete malpighianwm, appears only after 

 birth. In the negro, however, the edges of the nails, the 

 areola of the nipple, and the genital parts, begin to assume a 

 dark tinge on the third day, and by the fifth or sixth, the 

 black color has spread over the whole surface of the body. 

 The base of the umbilical cord also has a peculiar brownish 

 hue at birth. Researches by Sappey, however, show that the 

 deep layers of the epidermis always contain a small quantity 

 of pigment ; the differences of complexion observed between 

 different races are only due to the larger or smaller quantity of 

 this pigment: various influences may heighten its development 

 in the white races; such, for instance, as the prolonged action 

 of heat; in this case the solar rays do not give birth to 

 pigmentary granulations, as a new element, but simply occa- 

 sion the hypertrophy of those which already exist (Sap- 



pey). 1 



The other layers are offshoots from the malpighian layer; 

 its globules multiply constantly, and, by means of this physi- 

 ological proliferation, the globular elements which have 

 formed a part of the primitive layer, gradually withdraw from 

 the dermis, and form a succession of layers, the oldest of 

 which are always nearest the surface. "When these globules 

 extend a certain distance from the dermis, they appear to fall 

 suddenly into decay, and here the line is drawn between the 

 corneous layer and the rest of the epidermis ; this sudden death 

 is the fate common to all cells (excepting, perhaps, in such 

 growths as the nails, the globules of which always preserve 

 their nuclei), and, it appears from what we have seen, to the 

 epithelial cells also (intestine). These sudden changes are 

 not surprising, in some cases being much more marked: 

 instances have been known in which the hair, under the in- 



1 See L. H. Farabeuf, " De 1'Epiderme et des Epitheliums." 

 Paris, 1873, p. 265. 



