THE NERVOUS SYSTEM. 769 



quantities, too, of the exudations vary greatly. In some cases death 

 may occur with so slight a formation of exudate that to the naked eye 

 the pia mater may look quite normal or perhaps only moderately hyper- 



-3,^.^-V^ 11 



.;.,'-.;.,,'":.; 



*&- -~~" * f , }< 



\."-.x -.-:.:: ' 



./ r.. 



;-TE EXUDATIVE MEMXOITIS. 



Showing distention of the meshes of the pia mater of the brain with fluid, in which are leucocytes and ex- 

 foliated endothelium, the latter undergoing proliferation. 



seniic or redematous ; the microscope, however, in these cases will reveal 

 pus cells in small numbers, new-formed connective-tissue cells (Fig. 503 

 and Fig. 504), and sometimes flakes of fibrin in the meshes of the pia and 

 along the walls of the vessels. In other cases turbid serum in the meshes 

 of the membrane is all that can be seen, and the microscope shows the 

 turbidity to be due to pus cells or a small amount of fibrin. Again, 

 either with or without marked (Bdema of the pia mater, yellowish 

 stripes are seen along the sides of the veins, sometimes appearing like 

 faint turbid streaks, and at others dense, opaque, thick, and wide, and 

 almost concealing the vessels. These are due to the accumulation of 

 pus cells and fibrin in large quantities along the vessels, and are best 

 seen and most abundant around the larger veins which pass over the 



FIG. 504. ACCTE EXUDATIVE MENINGITIS. 



Proliferation of connective-tissue cells and extravasation of leucocytes in the adventitia of a small blood- 

 vessel of the pia mater. 



sulci. In still other cases the infiltration with pus and fibrin is so dense, 

 thick, and general that the brain tissues, convolutions, and most of 

 the vessels of the pia mater themselves are concealed by it. This pus is 

 usually of a greenish -yellow color, and is sometimes so thick as to form 

 49 



