Portal de Periódicos da CAPES

XXX. On the cutaneous pigmentary system of the frog

1858; Royal Society; Volume: 148; Linguagem: Inglês

10.1098/rstl.1858.0030

2053-9223

Joseph Lister,

Olfactory and Sensory Function Studies

The fact that the skin of the frog is capable of varying in colour, has been for some years known to German naturalists. The first account of the mechanism by which these changes are effected, appears to have been given by Professor Brücke, of Vienna, in 1852, and the subject has since been very carefully investigated by Dr. von Wittich of Königsberg, and Dr. E. Harless of Munich. All these observers describe the dark pigment as contained in stellate cells, each composed of a central part or body and several tubular offsets, which, subdividing minutely and anastomosing freely with one another and also with those of neighbouring cells, constitute a delicate network in the substance of the true skin. They describe the dark contents as sometimes concentrated in the bodies of the cells, at other times diffused throughout the branching processes, the skin of the creature being pale in the former case and dark in the latter. In the tree-frog the change from a dark to a pale state of the body generally was induced by bringing the creature into a bright light, by psychical excitement (as was supposed), or by galvanizing the spinal cord; and a similar effect was produced on a particular portion of the surface by irritating it mechanically, or with oil of turpentine, or by galvanism applied either directly to the part, or through branches of nerves leading to it. After the source of irritation was removed, the skin returned somewhat slowly to its former colour; and von Wittich noticed that when the paleness produced by direct irritation had passed off, the tint became deeper in the irritated spot than elsewhere. The esculent frog exhibited similar phenomena, but was less sensitive. The concentrated state of the pigment is attributed by all the observers above named to contraction of the cells, while the diffused condition is supposed due to their relaxation.