Note on the histology of fish skin (cod)

In the foregoing paper it has been shown that fish skins, and also the gelatin obtained from fish skins, behave in a somewhat different manner in acid and in alkaline solutions from mammalian skins (calf, ox, goat, etc.), and from the gelatin obtained from mammalian skins. How far this is due to actual chemical differences between the collagen and gelatin from the two sources, or, in the case of the skins, to any histological differences between fish and mammalian skins is not known. It was thought advantageous therefore to examine the histological structure of the type of fish skins used in the experimental work of the paper, viz., cod skins, and to see how far the differences in structure might account for the differences in behaviour between the fish and mammalian skins under the same experimental conditions. Samples of fresh cod skins were examined microscopically. Part of the same skin was dried and, after soaking in water for 4 days, was also examined. Portions of the dried skin were treated with sodium hydroxide as previously described (p. 281). Some of the portions were dried out ; others were treated with sulphur dioxide and then dried out. These dried sample were also soaked for 4 days and then examined microscopically. The fresh or soaked material was fixed in a 10 per cent. solution of formalin and sections were cut on the freezing microtome. The methods of staining used were as follows:─ (1) Ehrlich's hæmatoxylin and eosin to show cell nuclei and general fibrous structure. (2) Ehrlich's hæmatoxylin and scarlet red to show cell nuclei and any fat present. (3) Weight's resorcin fuchsin, to show elastic fibers and also to indicate the degree of degradation of the collagen.