When describing the substance of the skin, in the second section of CHAP. II, we mentioned a reticulated layer which covered the peripheral surface of the pa pilla., called by Bichat, the reticular portion, and by Cruikshank the membrane of the small-pox. The exist ence of this membrane, considered as a distinct layer of the integuments, seems not to have been ascertained before the appearance of Mr Cruikshauk's Experiments; and 13!c hat evidently confounds it with a more superfi cial layer, which is properly the rete mucosum or mucou,, network. This is usually described, not as a membrane, but as a stratum of a mucous or glairy fluid, deposited between the cuticle and the skin by the vessels of the latter. Previous to the time or Malpighi, it was not dis tinguished from the cuticle ; but that acute observer discovered that it was a distinct substance, and gave it the of C07111Z8 mucosum vel reticulare ; though, in honour of it was long called rete The greater part of this portion of the integuments appears to consist of a very delicate vascular and porous tissue, connected centrad with the skin, and nerob•rad with the cuticle by means of very slender filaments, though we are inclined to believe that the old opinion of its being composed of a mucous fluid is partly just, and that such a fluid is diffused over or through the tissue. With the nature of this substance we are unacquainted ; but perhaps it is similar to the oily fluid that has been detected by Vauquelin as forming the colouring matter of the hair.
It is now fully ascertained that the colour of the body depends on that of the rete 71111•OVall. This substance is black in the JVcgro ; reddish in the Mulatto, and proba bly in the nails e .?Im•rican ; brown in the Gypsy ; white, with a slight shade of red, in most Europeans ; and of a dead white in the Albino. In Fig. 5, of Plate XVIII, c, is represented the rete MUC0411111 of a Negro.
From the observations of Cruikshank, Bichat, and other late experimental anatomists, it appears that the integuments of the human body consist of at least six layers, viz. I, Cuticle ; 2, A peripheral layer similar to cuticle, but of a finer texture ; 3, Bete mucosum ; 4, Membrane of cutaneous eruptions; 5, Skin; 6, Cellular membrane.
The morbid appearances presented by the organs of integumation are extremely numerous, constituting the characteristics of those multifarious affections called Cutaneous Diseases. We shall notice only the inure general and important ; they will be considered hereaf ter in the articles MEDICINE and SURGERV.
The cuticle is often seen scaly. Sometimes the scales fall off, and leave a redness of the surface below, as in leprosy ; sometimes they accumulate, and render the cuticle very thick, hard, and insensible, as in that pe culiar affection called ichthyoas. Frequently the surface
of the cuticle is elevated into protuberances, which are sometimes soft, constituting what arc called NITHS; sometimes hard and callous, as in warts.
Alost of the morbid appearances of the integuments extend beyond the cuticle, taking the forms of rashes, as in the various ea an the mata, as measles, scarlet fever, nettle rash, Exc.; of bullx or bladders, as in erysipelas (St Anthony's fire, or rose); pen/deigns, or vesicular lever, and pompho/yx, or water blobes ; vesicles or blis ters, as in herpes, (ring-worm, shingles); varicella (or chicken-pock); miliary eruptions, aphth.e (or thrush), &c. and of pustules as in small-pox, cow-pox, itch, scald-head, &c.
For the best accounts of the structure of the integu ments, see Bichat's Gi at rale, tomes i. and iv.; Cruikshank's periments on th• Insensible Perspiration of the Human Body; Cutler's f.econs d'..Inatomie Com par6e, torn. ii. ; and White's ./ccount of the Regular Gradation in .flan, and in different inimals, S.cc.
The best accounts of the morbid appearances of the integuments will be found ill Willan's rrrilition and Treatm,•nt of Cutaneous OiSca.r:•S, and in Alibert's scription des Maladies de la reau, Of the ORGANS of IlErnonyeTios In the preceding chapters we have considered all those organs of the human body, that appear necessary for carrying on the various functions of man, considered as an individual, whose principal object is to support We, and to hold communication with the external bodies that surround him, and with other individuals or the same species, abstracted from the consideration of sex. We have described the organs which give firmness and support to the whole body, and which form the solid boundaries of its various cavities ; those by o Mich the whole body and its different parts are set in motion ; and those through the medium of which the body re ceives impressions Irom without, or communicates to the most distant organs the impulses by which the mind actuates them to motion. We have considered the or gans that arc subservient to the support of animal life, to the distribution of the fluids throughout the system, and the consequent nourishment of the whole (manic, and to the renovation of those principles of activity which had been lost during the accomplishment of these ends. We have examined the structure and uses of those organs which separate from the general mass of circulating fluids, the substances that are useful or ne cessary for carrying on the functions of other organs, and which convey out of the system, through the va rious emunctories, those which are hurtful or effete ; and we have, in the last chapter, described those organs which serve as a general covering and defence to the whole both.