Annual report : 1919/20 / King Edward VII Sanatorium, Midhurst.

  • King Edward VII Sanatorium (Midhurst, England)
Date:
1920
Catalogue details

Licence: Public Domain Mark

Credit: Annual report : 1919/20 / King Edward VII Sanatorium, Midhurst. Source: Wellcome Collection.

    13/32 (page 11)
    (b) On the Acid-fastness of Tubercle Bacilli.—The comparative efficiency of a large number of methods for staining tubercle bacilli was investigated by Bohm (1912).* Macalisterj (1912) compared the methods of Much, Herman, and Gassis with that of Ziehl-Neelsen. These observers came to the conclusion that the Ziehl-Neelsen method was for practical purposes the best, since the few others that gave equally good results were some¬ what more troublesome to carry out in practice. Both these investigators stained a series of sputums by the various methods, and estimated their relative efficiencies by the number of positives recorded to each. This furnishes a fair comparison for practical purposes in cases where there is a considerable difference in the results of the methods examined. The Ziehl- Neelsen method was used as a standard of comparison, but no indications were obtained as to the absolute value of the Ziehl-Neelsen method itself, i.e. the proportion of the total tubercle bacilli present which were demonstrated by this method. * It is known that the acid-fastness of tubercle bacilli in \ cultures is variable, the younger specimens being less acid-fast than the older. The examination of sputa stained by the Ziehl- Neelsen method reveals some degree of variability in staining amongst the individual tubercle bacilli in the preparation, and points to the fact that they are not all equally acid-fast. It is generally recognised that it is impossible to decolourise tubercle bacilli by prolonged treatment with mineral acids, but no exact estimates of the susceptibility of the bacilli to acids appear to have been attempted. The present investigation aims at obtaining accurate quantita¬ tive data as to the susceptibility of tubercle bacilli in sputum to the various acids commonly employed as decolourisers. The effect of sulphuric acid on tubercle bacilli stained with carbol- fuchsin was the first question taken up. The results are expressed as the percentage of tubercle bacilli decolourised in a given time by immersion in acid of a specified strength. Since, owing to the irregularity of distribution of tubercle bacilli in sputum, it is impossible to obtain accurate results by taking an average count of the bacilli per field before and after decolourisation, a method has been devised by means of which identical areas can be examined before and after treatment by decolourisers, and individual bacilli charted on a diagram ; this largely does away with the errors involved in striking an average, and gives unequivocal results. * Bohm; Centralbl. f. BaM., Abt. I., Orig. Ixii, 1912, p. 219, t Macalister: Brit. Med. Jouvn., Vol. ]]', 1912, p. 412.