EFFECTS OF HEAD IRRADIATION IN NEWBORN RATS 



65 



plexus, in addition to the capillary changes which were at times limited to 

 the plexus in the fourth ventricle, the parenchymal cells appeared sw^ollen 

 and cytoplasmic material more watery than normal, and the cells contained 

 relatively little granidar material. Acute inflammatoiy reactions noted in 

 the meninojes were obser\ed in most animals oiven over 300 r within the 

 first 8 postnatal days (Fig. 3). Tht- meningitis, characterized by neutro- 



FiG. 3. (a) .\ photomicrograph showing, in trans\erse section, the \iiitral mid- 

 pontile region in a 23-day-old rat that had been given 1000 r to the head on the first 

 postnatal day. Notice the thickened meningeal coverings (arrow) and the thickened 

 vascular channels of the pia mater. (X 32) (b) .\n enlargement of the block out- 

 lined in a, showing more clearly the thickened \ ascular walls (anows). The lumen of 

 the vessel on the right was almost completely obstructed. Thioninc stain (X 130) 

 (From Clemente et al.. 1960. p. 670.) 



