BIOLOGICAL ACTION OF LIGHT HILL 335 



to form thrombi which block the vessels (Argyll Cami^bell and L. 

 Hill). -While pigmented animals are jjrotected, albinos made sen- 

 sitive by injection of haematoporphyrin die after exposure to light. 

 Meyer Betz was daring enough to inject some haematoporphyrin 

 into himself and siiifered from oedema of the face and hands on 

 exiDOSure to light. He remained sensitive for weeks. It seems 

 possible that sensitization may prove useful in light therapy, but 

 great caution in dosage is required. Painting patches of lupus 

 with glycerin and eosin has been tried so as to endeavor to secure 

 a greater local effect from light treatment, but definite evidence for 

 this has not been found (A. Eidinow and L. Hill). 



Sudden exposure to ultra-violet rays stimulates to contraction 

 such an organ as the uterus of the guinea pig or the stomach of a 

 frog. The excised iris by pigment is made sensitive and contracts 

 on exposure to visible rays. Harmful ultra-violet rays do not pass 

 through the cornea and lens, and when the retina is damaged by 

 overexposure to an arc light or to sun (as in viewing an eclipse 

 without smoked glasses) it is injured by excess of visible rays act- 

 ing on its extremely sensitive substance. The lens may be damaged 

 by overheating through rays entering the eye through a large solid 

 angle and concentrated therein. Photo-electric effect produced by rays 

 acting on a specific retinal substance or substances may be the first 

 stage in the excitation of vision. Russ has claimed that the owl's 

 eye transmits ultra-violet rays. As far as concerns rays shorter 

 than 300 /t/x, this is not the case with the cat's eye, which has good 

 nocturnal vision, nor with the cod's eye, a fish which swims in dim 

 lights of somewhat deep water. Tested by putting the cornea in a 

 band of biologically active ultra-violet rays, using the cadmium 

 spark, none reach a fluorescent screen placed at a window 

 cut in the posterior part of the eye (A, Eidinow and L. Hill). 



It has been suggested that there is a biological interference be- 

 tween infra-red, or visible rays, and ultra-violet rays. Hess found 

 a longer daily exposure to the mercury-vapor lamp necessary in 

 order to prevent rickets in young rats (fed on a deficient diet) 

 when a glass screen was interposed which let red and yellow rays 

 through as well as ultra-violet, than was the case with a glass 

 screen which only let ultra-violet rays through. The photographs 

 of the spectra of the two screens seemed to show equality of the 

 ultra-violet radiation, but a difference in intensity is the most 

 probable explanation. Pech claims that both bleaching of cotton 

 and production of erythema by ultra-violet rays is delayed by a 

 concomitant beam of infra-red rays. Infusoria seemed to move 

 activel}^ longer in the light of a mercury-vapor lamp when red 



