Left-hand panel: histogram of reddening for the sample of 66 QSOs whose spectra were found to exhibit C i absorption (multi-colour). The colour/hash coding for the different C i-detected lines of sight relates to the best-fitting extinction law (red: SMC; blue: LMC; green: LMC2; purple: MW). The distribution of reddening from the QSO control sample (C.S.), i.e., the sum of the normalized distributions of individual QSO control samples, is displayed with dashed lines. Right-hand panel: same as in the left-hand panel but for the histogram of 2175 Å bump strengths. The distribution from the QSO control sample is well represented by a Gaussian profile (solid curve).