74 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



blood, or (6) connective-tissue cells may elaborate 

 it and deliver it secondarily to the epithelial cells. 

 That the pigment is not intrinsic to epithelial cells is 

 proved by the fact that colored skin grafted on a 

 white man soon turns white, and white skin grafted 

 on a colored person turns black. The fruitless at- 

 tempts to change one's color are well known. 



A melanotic sarcoma is a pigmented connective- 

 tissue tumor, very malignant, whose cells disseminate 

 very rapidly throughout the body, producing every- 

 where new tumors. These cells have their origin 

 from normal pigmented connective- tissue cells, and 

 therefore are supposed to come from birth-marks, or 

 the choroid of the eye, or the piamater of the brain. 

 The etiology of such tumors is unknown. Fortu- 

 nately they are rare. 



The facts to be remembered in regard to con- 

 nective tissues are : i . The easily stained round, or 

 oval, or spindle-shaped nucleus. 2. The cells are 

 loosely thrown together, not in compact layers or 

 strata. 3. The stellate cells, although the processes 

 are often inconspicuous and not readily detected. 



4. The tissue is vascular where cells are abundant. 



5. The absence of free nerve endings as among epi- 

 thelial cells. 6. They do not secrete as do the epi- 

 thelial cells. 



2. CARTILAGE. 



Cartilage is supporting tissue in which the inter- 

 cellular substance predominates and yields chondrin 

 upon boiling. The cartilage cells are typical con- 

 nective-tissue cells, and occupy lenticular spaces in 

 the matrix called lacuna. Cartilage is surrounded 

 by a dense connective-tissue membrane called the 



