TISSUES. 73 



parts, and also for the redness, which is due to the 

 extensive blood supply which is always associated 

 with this tissue. Such a swollen tumor represents 

 an induration and a congestion. In this manner a 

 whole or a part of an organ may be affected. The 

 connective-tissue fibers are absorbed with difficulty 

 or not at all, and a permanent mark or scar remains 

 as an evidence of the injury. In a healing wound, 

 particularly if infected, these fibers are abundantly 

 produced, and its redness is evidence of its extensive 

 vascularity or blood supply. Later, these fibers con- 

 tract, which occludes the blood, and then the color 

 changes from a red to a white scar that no medical 

 treatment can remove. 



Pigmentation is a most important subject. Pig- 

 ment appears, as a rule, in the cytoplasm of cells, 

 seldom between the cells. It is not confined to con- 

 nective-tissue cells, but is common to epithelial cells, 

 as the deep layer of the epidermis giving the color of 

 races ; is found in the retina cells, where it is always 

 black, and in hair and nails. It appears in the cyto- 

 plasm of muscle cells, particularly in old heart 

 muscle,where it is found near the ends of the nuclei, 

 and is nearly always present in nerve cells, giving a 

 gray color to this tissue. Pigmentation is an ac- 

 companiment of many diseases, particularly skin 

 diseases. It is also produced under the influence of 

 light, as freckles, that can only be removed by the 

 normal exfoliation of the epithelium. 



The production of pigment seems to depend upon 

 the blood. As blood is absent from epithelium there 

 are two theories as to the manner in which the cells 

 obtain it: (a) they may receive it directly from the 



