NORMAL HISTOLOGY. 



Pigment-cell from newt's skin. 



The immediate vicinity of the blood-vessels is a favorite locality 

 for pigment-cells, their arborescent processes often forming a net- 



work completely enclosing the 



FIG. 36. vessel. The supporting stroma 



of various organs of many of 

 the lower animals frequently 

 contains such cells, the liver 

 constantly presenting con- 

 spicuous groups of deeply-pig- 

 mented elements. Pigment- 

 cells are capable of spontaneous 

 movement, the changes in- 

 cluding not only alterations or 

 retractions affecting the pro- 



cesses phenomena directly influenced by the action of the light 

 but likewise decided alterations in position and location of the cells. 

 The granules of the dark-brown pigment are usually regarded as 

 composed of melanin derived from the coloring-matters of the blood; 

 recent investigations, however, render it probable that, while appar- 

 ently the same, the dark pigment found within the various tissues is by 

 no means always identical in composition. The isolated particles when 

 examined with high amplification are but slightly colored, the charac- 

 teristic tint appearing only when the pigment-granules are massed. 

 Whether the colored particles are taken up by the cells as pre-existing 

 pigment-granules, or whether they are produced within the proto- 

 plasm of the cell, is still undecided ; the evidence, however, seems to 

 favor the conclusion that the particles possess an extra-cellular origin. 

 The arrangement of the connective-tissue cells varies with 

 the age and density of the tissue. Where 

 the cells retain the FlG - 39- 



stellate type, a pro- FIG. 38- 



toplasmic net-work 

 extending through- 



Plate - like connective- 

 tissue cells found in ten- 

 don. 



Cell-spaces of dense con- 

 nective tissue in which the 

 cells lie : silvered ground- 

 substance ; from the cornea. 



Connective - tissue (corneal) corpus- 

 cles : these cells occupy the spaces 

 within the ground-substance. 



out the tissue is formed by the union of the processes ; examples of 

 such disposition are seen in young mucoid tissues, the cornea, and 

 other connective substances rich in cells. Parallel rows of closely- 



