Fig. 2
From: Adaption of a dermal in vitro method to investigate the uptake of chemicals across amphibian skin
Comparative overview of permeability coefficients of caffeine and testosterone applied to the skin of Xenopus laevis. Permeability coefficients are arranged as boxplots, separated into the different groups fresh and frozen stored skin samples from dorsal (=d) and ventral (=v) body sides; each boxplot is based on 4–7 skin samples (as specified in brackets behind indication of skin side beneath the boxplots), stemming from two animals (for testosterone frozen stored skin samples stemmed from four frogs); dashed gray line: conferring to Marzulli et al. [26], substances may be classified into five classes for estimation of their permeation rates according to the obtained permeability coefficients (<6 × 10−6-, 6 × 10−6 to 6 × 10−5, 6 × 10−5 to 6 × 10−4, 6 × 10−4 to 6 × 10−3, and >6 × 10−3-cm/h meaning very slow, slow, moderate, fast, and very fast, respectively); ns not significant; asterisks indicate level of significance and different letters indicate significant difference calculated as described in “Methods” section. An Additional file shows individual maximum permeability coefficients in detail (see Additional file 1)