CHAPTER XXIX 



Filtered Ultraviolet Radiation 

 Wood's Light 



THE use of filtered ultraviolet rays is important as an additional method 

 of investigating some mycoses and of determining the causative spe- 

 cies of fungus. The "black light" has been the subject of extensive investiga- 

 tion; it is used in many different industries, where substances such as cer- 

 tain minerals show characteristic fluorescent properties. Spurious currency, 

 forged checks and false covers over paintings may be revealed under the 

 filtered rays when the true nature would not be readily detected in day- 

 light. Margarot and Deveze first drew attention to the value of filtered 

 ultraviolet rays as a diagnostic aid in infections of the scalp with Micro- 

 sporum. 



1. SOURCE OF ULTRAVIOLET RAYS 



As a rule, it is not practicable to use the sun's rays as a source of ultraviolet 

 rays. However, any of the ordinary office lamps for the production of ultra- 

 violet rays, whether air-cooled or water-cooled, is suitable for this purpose. 

 Less expensive lamps are also serviceable, although the heat generated 

 is a drawback. Davidson and his co-workers have devised two different 

 portable lamps which have proved satisfactory for the detection of tinea 

 capitis. The directions given for their construction, however, are rather 

 vague in certain particulars. Another source of light is a commercial lamp 

 used for indoor photography in which there is an overloaded filament which 

 produces the requisite bright rays but has a correspondingly shorter life 

 than the filament of an ordinary lamp. Although the intensity of optimum 

 rays from its beam is not so great as with the aforementioned lamps, the 

 photographic lamp is nevertheless a satisfactory substitute for the usual 

 ultraviolet lamp. 



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