NORMAL HISTOLOGY. 



FIG. 36. 



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 

 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- 



Pigment-ceii from newt's skin. eluding 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 were formerly regarded 

 as composed of melanin derived from the coloring-matters of the 

 blood ; recent investigations, however, render it probable that, while 

 apparently 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 characteristic tint appearing only when the pigment-gran- 

 ules are massed. Exceptionally the colored particles are taken up 

 by the cells as pre-existing pigment-granules ; more usually, how- 

 ever, they are produced within the protoplasm of the cell by elabo- 

 ration from special substances held in solution. 



The arrangement of the connective-tissue cells varies with 

 the age and density of the tissue. Where 



the cells retain the 

 stellate type, a pro- 

 toplasmic net-work 

 extending through- 



FIG. 39. 



FIG. 38. 



Plate - like connective- 

 tissue cells found in ten- 

 don. 



Cell-spaces of dense con- 

 nective tissue in which the 



Connective - tissue (corneal) corpus- 

 :les : these cells occupy the spaces 



cells lie : silvered ground- within the ground-substance, 

 substance ; from the cornea. 



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- 



