212 ANNUAL EEPORT SMITHSONIAN INSTITDTION, 1942 



pane glass so as to transmit into the interior biologically active rays, 

 and in the manufacture of equipment to be used for an artificial 

 source of ultraviolet light. Furthermore most ultraviolet light is 

 absorbed by thin layers of fluids containing proteins or turbid mate- 

 rial, by layers of oil and grease, and also by tissue cells. Tissue is 

 not penetrated more than 1 millimeter (0.039 of an inch) in depth. 

 Very short wave-length radiations are absorbed by air in the produc- 

 tion of ozone. These facts must be considered in the practical use 

 of ultraviolet light as a bactericidal agent. 



GENERATING ULTRAVIOLET LIGHT 



Artificially generated light is just as effective as the corresponding 

 rays of sunlight that possess the same wave lengths or the same in- 

 tensity. The source of ultraviolet light has very little influence 

 upon the result, providing the wave lengths or intensity are identical. 

 The sun, the natural generator of ultraviolet light, is not always 

 available. Even when available the natural germicidal ultraviolet 

 rays cannot be harnessed conveniently to be supplied to environ- 

 ments not reached by sunlight. It therefore became necessary to 

 provide some means of artificially generating ultraviolet light so as 

 to make it available whenever and wherever needed. When investi- 

 gators, especially during the past two decades, reported marked de- 

 structive effects of different microorganisms by controlled laboratory 

 tests using special artificially generated short wave lengths of ultra- 

 violet light, the latter was hailed as the ideal sterilizing agent and 

 its use was advocated far and wide. As in other similar cases, not 

 recognizing that its application is bounded by distinct limitations, the 

 use of ultraviolet light was soon discarded owing to its abuses, and 

 also to the fact that many of the ultraviolet generators available 

 were not only expensive but produced radiations which were un- 

 suitable as germicidal agents. 



RENTSCHLERIZING PROCESS 



After several years of careful research and extensive experimental 

 work, Dr. Harvey C. Rentschler, engineer and research director, 

 Dr. Robert F. James, bacteriologist, and other workers associated 

 with Westinghouse Lamp Division succeeded in designing equip- 

 ment for ultraviolet radiation which is inexpensive and overcomes 

 most of the objections made against other previously introduced 

 ultraviolet generators. The radiations produced by the latter were 

 found to cover broad rather than selective bands of wave lengths, 

 which were found to be most effective as germicidal agents. In 

 many of the generators used previously, an appreciable amount of 

 infrared rays was generated, resulting in the production of high 

 temperatures during operation. Such operation in refrigerated com- 



