AYERS AND JOHNSON: DESTRUCTION OF BACTERIA 163 



milk. This was probably due to the fact that the cream when 

 picked up by the revolving drums was in a thicker layer than 

 was the milk. 



9. When milk was exposed under conditions suitable for a 

 satisfactory reduction of the bacteria by the ultraviolet rays 

 there was also produced an abnormal, disagreeable flavor. This 

 flavor would render the milk unsaleable. 



10. A large percentage of the bacteria in normally dirty and 

 artificially infected milk bottles were destroyed by exposure to 

 the rays. The best results were obtained when the bottles were 

 exposed directly under the lamp, the top of the bottle being about 

 4 inches from the lamp tube. When bottles were exposed on one 

 side of the lamp and not directly under it, poor results were 

 obtained. It was not possible to completely sterilize the bottles 

 even after a ten minutes' exposure. 



CONCLUSIONS 



The experiments indicate that with quartz mercury vapor 

 lamps of the present power and construction it would not be pos- 

 sible to completely sterilize milk by the ultraviolet 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 

 that the pathogenic bacteria would be destroyed. This process, 

 however, would not afford the same security as does proper 

 pasteurization. Then, again, it would be difficult on a commercial 

 scale to control constantly the factors which influence the bacteri- 

 cidal action of the rays. Aside from these points the disagree- 

 able flavor imparted to the milk by exposure to the rays renders 

 the process impracticable on a commercial scale. 



