Soft stabilization has an important role in the treatment of the degenerative lumbar spine. Fusion of one or two motion segments may not make a big difference in the total range of motion of the lumbar spine, but preserving flexibility of a motion segment may prevent adjacent segment disease and may permit disc replacement, even when facet joints need to be excised. A favourable environment is created in the motion segment by unloading the disc and permitting near normal motion, the disc may be able to repair itself or may supplement reparative potential of gene therapy.

Cultures of Vibrio cholerae 01, biotype El Tor, from the current epidemic of cholera in the Western Hemisphere, and of the new V. cholerae serogroup 0139, from the current outbreak in India and Bangladesh, revealed marked colonial heterogeneity when received by the authors. By comparison with reference colony types, using a stereoscope and transmitted oblique illumination, colonies of approximately 10 different degrees of opacity could be distinguished. In contrast, strains freshly isolated from patients and rapidly and carefully preserved were more homogeneous although still differentiable by this technique. These (and older) observations prompted the questions: (1) why is a V. cholerae colony opaque or translucent? and (2) what benefit is it to the vibrios to vary their colonial appearance? The observed changes in colonial opacity, which are reversible, are sometimes (rarely) accompanied by changes in virulence for infant rabbits and, more frequently, by other phenotypic variations including the ability to produce poly-p-hydroxybutyrate inclusion bodies on glycerol-containing medium, the degree of encapsulation in 0139, changes in outer-membrane proteins, alteration in lipopolysaccharide structure, changes in expression of glycolytic pathways, and differences in ability to survive under adverse conditions. Colonial variations in choleragenic vibrios are phenotypically multifactorial. The genetic mechanisms(s) underlying the observed phenotypic changes remain to be defined.Keywords : Vibrio cholerae, colonial variation, opacity, poly-P-hydroxybutyrate (PHB), capsules INTRODUCTIONCholera vibrios have long been known to be mercurial in their ability to exhibit variations in colonial morphology. Robert Koch was the first to observe that the colonial appearance of cholera vibrios was distinct from that of other bacterial species (Pollitzer, 1959, p. 125). Soon thereafter, Kolle and Gotschlich (Pollitzer, 1959, pp. 452-456), and subsequently others, noted that vibrio subcultures contained opaque (0) and translucent (T) colonial variants. Lankford (1960) observed that nearly all colonies of classical biotype Vibrio cholerae on primary culture from patients in Calcutta, India, in 1953, and in Bangkok, Thailand, in 1958, were of a single characteristic ' typically opaque and striated ' colony type, whereas most stock cultures of V. cholerae Abbreviations: LOS, lipooligosaccharide; MR, methyl red; OU, opacity unit; PHB, poly-P-hydroxybutyrate; VP, Voges-Proskauer.were mixtures of colony types or pure types differing from each other. Colonies which deviated from the ' typical ' colony type usually had reduced virulence for 13-d-old chicken embryos (Lankford, 1960 ;Gardner et al., 1964). The apparent homogeneity of fresh isolates has also been the author's (R. A. F.'s) experience during cholera epidemics of El Tor and classical biotypes in the Philippines, India, Vietnam and Thailand during the period from 1961to 1967. In 1966, it was noted (Finkelstein, 1966 that stock cultures of El Tor biotype V. cholerae sent f...