274 An Introduction to Medical Mycology 



2. FILTER 



The type and thickness of the glass filter through which the ultraviolet 

 rays pass are of great importance. This is especially true when the fluo- 

 rescent colorations of cultures of fungi are being observed. Divergent results 

 may be obtained by different observers owing to a difference in the type 

 of glass filter or in its thickness. We have found that the wavelengths in 

 the near portion of the ultraviolet part of the spectrum (in the region of 

 3,650 angstroms) offer optimum fluorescent value. Many different types 

 of glass have been tried; an adequate type is the Corning glass violet ultra, 

 no. 586, polished to a thickness of between 4 and 5 mm. In its molded form 

 it is usually from 7 to 8 mm. thick, and unless the source of light is ex- 

 tremely powerful, not enough ultraviolet rays are transmitted to produce the 

 desired results. The glass is sodium barium silicate containing slightly less 

 than 9 per cent nickel oxide. As the glass is not heat resistant, care must 

 be exercised that overheating does not take place, or cracking will result. 



3. EXCLUSION OF UNWANTED RAYS 



The room in which the examination is made must be darkened, and in 

 addition most of the visible rays from the ultraviolet lamp must be ex- 

 cluded by a suitable attachment, so that only the rays of light which are 

 not absorbed will pass through the filter. A tinsmith's services may be 

 utilized, or a molded copper attachment may be fitted to the lamp, leav- 

 ing an open slot for the filter. Mr. Harry Ashmore, an engineer, made 

 a satisfactory attachment of this type for us. When the source of light 

 generates considerable heat, suitable provision must be made for ventilation. 

 Some commercial lamps are now sold with attachments for the exclusion 

 of the unwanted rays. 



The unit here described is light, easily attached and detached and readily 

 stored, and it has proved durable in our hands. Any of the better makes 

 of lamp for the production of ultraviolet rays may be used as a source of 

 radiation. The attachment is constructed of 1 sq. yd. of light-proof black 

 rubberized focusing cloth (obtainable at a camera shop). A hole 5 in. 

 (12.5 cm.) square or smaller is cut near the center of the cloth, the size 

 depending on the size of the glass filter. It is suggested that the 5 in. hole 

 be used when the glass filter is 6)i in. (16.5 cm.) square. The edges of the 

 hole are hemmed. Then the glass filter is placed over this hole, overlapping 

 the cloth on each side. Elastic loops arc sewed diagonally across the four 

 corners to hold the glass in place. If the fit is snug, no light will seep around 



