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body of each cell to its remotest ramifications, and their close packing there, were an act such as a living organism alone could have effected. Pigmentary concentration and diffusion were vital functions of a profound character concerned with the relative distribution of different constituents of the cells. Yet from the very happy circumstance of the conspicuousness of the pigment, the results of their activity could be observed with the utmost facility, and their behaviour in relation to inflammatory congestion easily studied even under a low magnifying power.
The pigment cells pervade the skin and subcutaneous tissue of which the frog's web consists, and are especially numerous about the blood-vessels, round which their branches twine abundantly. They must, therefore, be acted on along with the vascular parietes by anything applied to the surface of the membrane. And to state shortly the result of many experiments, I found that any agency, physical or chemical, which caused the blood-corpuscles to lag behind the liquor sanguinis in the part on which it operated rendered the pigment cells in that particular area incapable of discharging their functions. Whatever might be their state at the time of the experiment, whether in full diffusion, complete concentration, or any intermediate condition, so they remained in the irritated spot, while in surrounding parts of the web, as in the body generally, they changed as usual in obedience to differences of illumination or other circumstances. At the same time they were not killed:
