FLUORESCEIN AS INDICATOR OF BRAIN INJURY 371 



Fig. 2. A "Land" camera roentgenogram of a rat's head with tlie image of the 2.0 

 X 25.5 mm beam superimposed. 



between the aperture and the area of the brain to be studied was kept con- 

 stant ( L75 in.) . 



Fkiorescein stainin^ of the damaged brain tissue was accompHshed by 

 intravenous administration of fluorescein sodium ( 100 mg per ml, pH 8.2) 

 under ether anesthesia of 10 mo- per 60 2,m body weight. After 45 minutes 

 the animal was anesthetized with ether, and the head was removed by Guillo- 

 tine and immediately frozen in liquid nitrogen. The head was then sectioned 

 on a high-speed handsaw in the sagittal plane, which was 1.75 in. from the 

 aperture at the time of irradiation. The cut sin-face was polished by holding 

 it under rimning water until free of all dust fragments, but not long enough 

 to melt the tissue. The two halves were examined in a dark room imder 

 uItra\iolet light while solidly frozen. A \isual estimation of the intensity of 

 the fluorescent band was recorded. Evaluation of the fluorescein staining 

 was made on the basis of an arbitrary scale from 1^- to 4+, with 1-|- being 

 faintly \isible and 4-|- being intense. When subsequent histologic examina- 

 tion was desired, the frozen brain was immersed directly in formalin and 

 processed in the usual way. Rapid freezing with liquid nitrogen did not 

 seriously interfere with later microscopic evaluation of the tissue. Micro- 

 scopic examination was also made of brain tissue which had not been sub- 

 jected to freezing to insure accurate interpretation. The skull vvas carefully 



