The structure of the _cutis_ is peculiarly curious, and may justly be considered as a continued _secretory_ and _excretory gland_; or more properly, like the bark of a tree; for whilst there is continual transpiration from the body, it, at the same time, is capable to absorb the subtile particles of whatever surrounds it, and exclude the grosser. Over the whole surface are innumerable little _pores_, which are nothing but the little openings of the various lymphatics, and of the blood vessels corresponding with their peculiar _glandules_, called the _milliary glans_; between those on the hairy parts, the hair is planted as it were, with their distinct roots, corresponding with the hue of the subject they belong to. These _pores_ widen or contract according to the internal or external warmth of the body; which when they contract, cause a kind of roughness, or continuation of little warts; and on the contrary, when dilated, smooth the skin. Next to this follows the fat skin, or _membrana adiposa_; which is a continuation of cells, wherein the fat is contained, and has an immediate communication with the neighbouring blood and lymphatic vessels. This part is not universal, for some parts of the face, the genitals, &c. are without it. The last of all is the _membranosa_, a thin parchment-like texture, which adheres spontaneously to whatever part it covers, either _periosteum_, the _tendons_, _ligaments_, or _muscles_. These are the four principal divisions of the skin; but that which is the principal, is the second mentioned, namely, the _cutis_; on which I shall have occasion to offer something hereafter, that may prove of the greatest advantage to the sea-faring people, for whose benefit I have particularly intended these Lectures. ------------------------------------------- SECT. IX. _Of the External Senses._ Feeling is the universal sensation of the nerves, on which all other senses depend, as the subtile spring of life itself. What it is, and whence it proceeds, has already in the foregoing been explained; namely, a sensation of the nerves, by which we perceive an idea of _hard_ or _soft_, _wet_ or _dry_, _hot_ or _cold_, or in general terms, _pleasure_ or _pain_. The peculiar seat thereof seems to be placed at the ends of our fingers; whether this is the absolute seat ordained by nature, or rendered so by custom, is not my business here to enquire; perhaps, both conjoin to make it there most perfect, as best suited for that purpose.