398 Sensation of Light produced ly Radium Rays. [Sept. 20, 



Some measurements of the screening power of various tissues were 

 made with a Curie electroscope. The numbers give the rate of leak 

 in divisions of the scale per second. The tissues were from a freshly 

 killed rabbit. 5 milligrammes of radium bromide were used, enclosed 

 in a lead capsule having an aperture 4 mm. in diameter on one side. 



Lead, 0-2 min. thick 25-0 



0-4 18-0 



2-3 11-3 



Skin of back, 0-8 mm. thick 20'5 



(shaved), 0-8 mm. thick ... 22'0 



Eyelid, 0'7 mm. thick 17-2 



Nictitating membrane, 0*8 mm. thick ... 28*6 



Iris 28-6 



Lens, 7 '5 mm. thick 14'0 



Sclerotic *| 



Choroid > 23'0 



Ketina J 



Sclerotic < 0'5 mm. thick 36*3 



Entire eyeball 11-5 



Muscle (skeletal), 3'0 mm. thick 19'0 



These figures show a remarkable difference in stopping power between 

 the eyelid and the nictitating membrane, in favour of the former, which 

 equals 0'4 mm. of lead. The screening power of the eyelid is also 

 noticeably greater than that of the skin of the back, although the latter 

 is the thicker. 



