Examination of smears for tubercle bacilli by fluorescence microscopy.

I n underdeveloped countries, laboratory faci l i ties for the bacterio­ logical d iagnosis of tubercu losis are, at present , very l imited . Cultural methods are un l i kely to be used on a large scale for many years to come. It is , therefore, important to investigate the most economical method of examin ing smears for tubercle baci l l i . Fluorescence microscopy was introduced by H agemann ( 1 937) and has since been described by many authors, incl uding Tan ner ( 1 94 1 , 1 948), Line and Shaughnessy ( 1 94 1 ), Lempert ( 1 944), Norman and Jelks ( 1 945), Clegg and Foster-Carter ( 1 946), Wilson ( 1 952), Von Haebler and Murray ( 1 954), and Needham ( 1 957). The great advan­ tage claimed for th is method i s that stained baci l l i can be detected using a much lower magnification than with the usual Ziehl-Neelsen method. Considerable t ime is saved i n examin ing smears and larger areas can be searched. The method has not been widely employed for two reasons. I n the first place, the l ight source must be very bright and many of the optical systems described previously have only supplied sufficient light if the equipment was used in a darkened room. Secondly, some workers (R itterhoff and Bowman, 1 945 ; Kuster, 1 939 ; Ho lm and Plum, 1 943) consider that false positive results can be obtained, s ince some smears may contain small natural ly fluorescent particles which can be confused with bacil l i . Equipment for fluorescence microscopy that can b e used in normal daylight has been in use at t he Tuberculosis Chemotherapy Centre , Madras, for over two years. When it was first introduced, a comparison between this method and the . convent ional Ziehl ­ Neelsen method was undertaken to test their relative sensitivities, and to see whether fluorescence microscopy yielded false posi t ive results. The results of this comparison are described .