BIOLOGICAL ACTION OF LIGHT HILL 333 



direct sun. Dorno at Davos showed that this was so using a cad- 

 mium photo-electric cell for recording the ultra-violet radiation. 

 Even with the sun at its zenith, the ultra-violet radiation from it is 

 only about 90 per cent of that from the blue sky. With the low 

 sun, the sky yields far the more. 



Smoke pollution robs us of half or more of the ultra-violet rays. 

 AVhile seeking to abolish this evil, we require to make the loss good 

 by the use of artificial sunlight baths. Screened as he is by window 

 glass, clothes, fog, and smoke, the citizen is cut off from ultra-violet 

 rays almost wholly in winter, and in consequence his general health 

 and resistance to disease goes down. The evil is enhanced by indoor 

 life spent in heated stagnant air of rooms, and by lack of open air, 

 exercise, and by a diet deficient in vitamins. Thus the resistance 

 to catarrhal infections, which spread in the crowded stagnant air 

 of rooms, is lowered. Those who live open-air lives and are well 

 fed, exposed however much they are to weather, are far less often 

 attacked. 



It has already been stated that the hsemobactericidal power of the 

 blood (as tested in vitro) is put up in an animal by an exposure to 

 ultra-violet radiation which is sufficient to produce erythema. It 

 has also been found by A. Eidinow that if a little blood is with- 

 drawn from an animal, irradiated by rotation in a quartz flask, and 

 then put back again into the animal, this puts up the hsemobacteri- 

 cidal power, and yet the irradiated blood itself has this power 

 actually destroyed in itself by radiation. The putting up of the 

 haimobactericidal power depends on the corpuscles and not on the 

 serum. In man it is naturally high, and can be put up less than in 

 such animals as rabbits and pigs. It is known that ferments, 

 serums, agglutinins, and the anaphylactic power of blood are alike 

 destroyed by ultraviolet radiation in vitro. 



Recent research on rickets has shown that the diseased calcifica- 

 tion of the growing bones results from a diet deficient in antirachitic 

 substance and lack of ultra-violet rays. If young rats are put on 

 a diet deficient in antirachitic substance and having a minimum of 

 salts of phosphorus, the latter is not absorbed from the gut. Either 

 the addition of antirachitic substance in cod-liver oil or ultra-violet 

 radiation for a few minutes a day will wholly stop rickets developing 

 and cause a minimal amount of phosphorus in the diet to be ab- 

 sorbed and utilized in bone building (A. Webster). It has been 

 proved that the antirachitic substance present in cod-liver oil is not 

 vitamin A, and that it can be put into an inactive food by ultra- 

 violet radiation (Hess, Steenbock). Thus, inactive linseed oil, 

 casein, flour, and lettuce leaves can be made effective as cod-liver oil 

 in preventing rickets, b}^ rotating them in a quartz flask in front of 



