Ultra-violet Rays. 201 



longed exposure of milk to such rays. Seiffert passes the milk in 

 broad bottles along the illuminating bodies, allowing the rays to 

 act upon the milk for about two minutes. He employed Leyden 

 jars fitted with aluminum or cadmium points, which are charged 

 with a current of high tension through an inductor which dis- 

 charges mutually. Gerber and Hirschli used for sterilization the 

 uviol light which is rich in ultra-violet rays; he was unable how- 

 ever to demonstrate a marked reduction of the bacterial content 

 by subjecting a layer of milk of 1 mm. thickness to its influence, 

 whereas Finkelstein and Lobeck, Henri and Stodel, Billon and 

 Daguerre obtained good results with the ultra-violet rays from 

 mercury and quartz lamps. According to Billon and Daguerre 

 sterilization may also be accomplished when milk is exposed to 

 white light in violet glasses. The action is the best when the white 

 light is split up by a prism. 



Romer and Sames, who also conducted experiments on the 

 bactericidal action of ultra-violet light proved that market milk 

 which has been exposed to the rays of a Heraus' mercury-quartz 

 lamp of 6 ampere strength in a quartz alembic (at a distance of 

 15 cm. from the source of light the action of which has been in- 

 creased by a reflector) caused a reduction from 98,900 original 

 bacteria after one hour of exposure to 16,500 bacteria; after 1% 

 hours to 8750 ; after 21 2 hours to 2,050 bacteria. The taste of the 

 milk was pronouncedly irritating. In a second test the number of 

 bacteria diminished from 111,800 to 94,000 in 10 minutes, and to 

 65,500 in 20 minutes. On the surface of the milk a yellowish scum 

 forms. The peroxydase reaction of the milk is destroyed after a 

 prolonged exposure to such light. 



[The experiments of Avers and Johnson indicate that with 

 quartz mercury vapor lamps of the present power and construc- 

 tion it wolild not be possible commercially to completely sterilize 

 milk by the ultra-violet rays. 



It might be possible to obtain bacterial reductions as great as 

 by pasteurization even on a commercial scale by the use of large 

 revolving drums and a number of lamps. However, in milk so 

 treated there would be no assurance of the complete destruction 

 of pathogenic organisms since the rays do not seem to exert any 

 selective destructive action on vegetative cells. Of course since 

 pathogenic organisms might be assumed to be present in a small 

 number in proportion to the total bacteria in milk, if 99.9 per cent, 

 of the organisms present were destroyed, it might be assumed 

 that the pathogenic bacteria would be destroyed. This process, 

 however, would not afford the same security as does proper pas- 

 teurization. Then, again, it would be difficult on a large com- 

 mercial scale to constantly control the factors which influence the 

 bactericidal action of the rays. 



It is also doubtful if the lamps could be made to successfully 



