VARIATION 



417 



heaped-up and convoluted, have a roughish granular surface, and tend to be 

 surrounded by a spreading veil-like peripheral extension (Fig. 78). In glycerol 

 broth the smooth forms may grow diffusely throughout the medium, they may 

 form a thin, smooth surface pellicle, or they may cover the bottom of the flask 

 with a reticulated veil-like growth ; the rough forms usually grow as a thick 

 wrinkled surface pellicle unaccompanied by turbidity. Morphologically, smooth 

 strains consist of fairly long, curved, slender, sometimes beaded bacilli, lying more 

 or less parallel to one another and occurring in bundles (Fig. 79) ; less often 

 they are rather short, stout, or ovoid bacilli, staining evenly, and arranged singly 

 or in groups (Fig. 80). Rough strains, on the other hand, consist of rather 

 short, sometimes ovoid, bacilli or cocco- 

 bacilli, arranged in Chinese letter forms and 

 in dense masses (Fig. 81). This morpho- 

 logical difference in the arrangement of the 

 smooth and rough types is similar to that 

 described by Nutt (1927) and Wilson (1930) 

 for Salm. typhi-murium, and by Soule (1928) 

 for B. anthracis and B. suhtilis. It has 

 been well pictured by Schwabacher (19336) 

 and Wyckoff (1934) for saprophytic acid-fast 

 and cold-blooded tubercle bacilli respectively. 

 It depends essentially on the mode of 

 division. The bacilli of the smooth type 

 separate completely after division, and slip 

 past each other so as to come to lie in par- 

 allel. The bacilli of the rough type exhibit 

 an angular division, the organisms not sep- 

 arating completely but coming to lie at an 

 obtuse angle to each other, resembling a green- 

 stick fracture, or forming long tangled masses 

 which become heaped-up and convoluted as 

 growth continues. It is hardly necessary to 

 add that many intermediate forms occur, 

 partaking of some smooth and some rough 

 characteristics. 



Whether the smooth and rough types 

 differ metabolically, antigenically, and in 

 virulence, it is impossible to say definitely 

 at present. Many workers assert that the smooth type of tubercle bacillus is 

 more virulent than the rough, but further evidence is desirable on this point. 



(References : Petroff 1927, Petroff, Branch, and Steenken 1927a, b, Petroff and 

 Steenken 1930, 1935, Kraus and Gerlach 1929, Uhlenhuth and Seiffert 1930, Begbie 

 1930, 1931, Dreyer and VoUum 1931, Reed and Rice 1931a, b, Rice and Reed 1931, 

 Rice 1931, Toda 1931, Seiffert 1932, Schwabacher 19336, Seibert, Long, and Morley 

 1933, Wyckoff 1934, Meiszner and Prausnitz 1934, Steenken et al. 1934, Birkhaug 

 1935, Denys 1935, Shaffer 1935, Smithburn 1935.) 



Resistance. — Acid-fast bacilli possess much the same degree of susceptibility 

 to heat as other non-sporing bacteria, but a rather higher degree of resistance to 

 chemical disinfectants. This behaviour is probably related to their content of 



P.B. P 



Fig. 77. — Saprophytic acid-fast bacilli. 



Left : smooth strain, showing raised, 

 confluent, butyrous growth, with 

 smooth, glistening surface. 

 Right : rough strain, showing raised, 

 confluent friable, heaped-up growth, 

 with dry, dull, rough surface. 

 Glycerol egg, 2 months, 37° C. 



