74 AIDS TO BACTERIOLOGY 



described by Cowie, and the name is now generally held 

 to include a number of allied organisms. Inoculation of 

 animals gives negative results. Czaplewski found it to 

 grow, though with difficulty, on serum, glycerin agar, 

 and in broth. Subcultures grow more freely. Muir and 

 Ritchie first showed that after staining and decolorising 

 with acid in the Ziehl-Neelsen method, a minute's ex- 

 posure to alcohol sufficed to remove the red stain from 

 smegma bacilli, and thus to prevent their being mistaken 

 for tubercle bacilli of which there is sometimes a risk, 

 especially in the examination of urine. In practice, 

 HouselPs combination of alcohol with the acid is most 

 frequently used (p. 61). 



Pappenheim's solution* has been recommended for 

 decolorising acid-fast bacilli other than tubercle after 

 fuchsin staining and washing, but it appears to have little, 

 if any, advantage over acid alcohol. 



Other Acid-Fast Organisms. 



A number of acid-fast bacilli have been found in milk, 

 butter, manure, and grass. Most of them grow freely on 

 ordinary media at room temperature, often producing a 

 pigment, yellow or brown. The best known among them 

 are the Timothy-grass bacillus (p. 159) and the ' Mist- 

 bacillus ' of manure. Some are pathogenic to guinea- 

 pigs, and the lesions produced may simulate those of 

 tuberculosis to some extent. 



Petri and Rabinowitch's ' butter bacillus ' is found in 

 butter fairly frequently, and when intraperitoneally 

 injected with butter into guinea-pigs produces nodules 

 that may be confused with tubercles. 



Acid-fast organisms have been found in sputum when 

 tuberculosis could be negatived on clinical and other 

 grounds. A hint as to their true character may be 

 sometimes obtained from the very small number seen on 

 prolonged search. Doubt as to identity should also be 

 expressed when the shape and size are not those usually 

 found in the case of the tubercle bacillus. Acid-fast 

 bacilli have been described in bronchitis and pulmonary 



* Pappenheim's solution, 1 part of corallin (rosolic acid) in 

 100 parts of absolute alcohol, to which methylene blue is added 

 to saturation; 20 parts of glycerin arc then added. 



