EPITHELIOMA. 369 



four varieties of abnormal pigmentation in the skin ; these 

 are — 



1. Simple pigmentation of the rete Malpiglui witliout marked 

 changes in the cutis (freckles, &c.). 



2. Pigmentation of the cutis without marked changes in the 

 rete Malpighii and the epidermis. 



3. Pigmentation of the rete where it invests a colourless 

 overgrowth of the papillary body. 



4. Pigmentation of the rete associated \Yith a simultaneous 

 deposit of pigment in a hyperplastic cutis. 



The three last categories include all varieties of the pigmented 

 mole ; the two last are included in the pigmented warts. The 

 pigment is deposited in the form of yellow, brown, or black 

 granules, partly in the cells of the rete Malpigiiii and connective 

 tissue, partly outside them, freely distributed throughout the 

 connective tissue of the papillary body. It sometimes accumu- 

 lates in such quantities as entirely to mask all peculiarities of 

 structure; nothing but pigment-granules boing visible. These 

 form long striae in the substance of the cutis, accompanying the 

 larger afterent and eiferent vessels. 



It is very unusual to find, besides tlic pigmentation of the 

 rete Malpighii, the nuclei of the older epidermic cells of a uni- 

 form black colour ; indeed the nuclei, even of pigmented cells, 

 are generally free from colouring-matter. I have observed this 

 i:)henomenon on one occasion only ; but I have failed to find any 

 reference to it in books. 



y. Heteroplastic Growths. 



§ 313. Two of the most important lietcroplastic growths 

 vrhich affect the skin originate in the papillary body, or in the 

 epidermis and papillary body together, while the remainder have 

 their seat in the cerium proper. The growtlis in question are 

 epithelial cancer and sarcoma. 



Epithelioma of the skin is very common ; hence we took it 

 as our type of the disease, in § 164. Here tliercfore I will con- 

 fine myself to the discussion of a few points, which were passed 

 over on that occasion. And first a few words concerning the 

 local etiology of the growth. 



Epithelioma of the skin occurs by preference at the junctio:i 



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