CUTANEOUS SYSTEM. 



2i9 



prsat excellence, and by some preferred to all 

 ouiers. The sour and sweet sops of the West Indies 

 are the muriated and squamose fruited custard apples ; 

 and are found useful even in that region of tine fruit- 

 Some of the species have fruited in our stoves ; and 

 no doubt were their culture more attended to, by 

 working the plants, and allowing space for their roots 

 and branches, the fruit may be brought to a conside- 

 rable degree of perfection. These plants require a 

 rich loamy soil, and are propagated by ripe cuttings 

 struck in sand. 



CUTANEOUS SYSTEM, comprehends the J 

 skin and its appendages, hair, wool, bristles, spines, 

 horn, hoofs, feathers, shells, crusts, scales, and other 

 analogous structures. 



Tiie skin is composed of three layers of integu- 

 ments viz., the Epidermis, or cuticle ; the Rcte 

 witwfium, or mucous web ; and the Cutis vera, or true 

 skin. 



The epidermis, or cuticle, which is the external 

 layer, is a dense semi-transparent, partially elastic 

 membrane, which is common to all animal and 

 vegetable bodies. It is everywhere continuous in its 

 course, being reflected inwards into the mouth, 

 nostrils, windpipe, gullet, and other open passages. 

 By Dr. Munro, it was traced down as far as the 

 cardiac region (upper portion) of the stomach of a 

 horse, and by many physiologists it is supposed to line 

 the whole tract of the alimentary canal. It invests 

 the roots, stems, leaves, and flowers of all plants, 

 forming an external covering, which protects them 

 from the action of fluids, and from the extraneous 

 effluvia which are constantly floating in the atmo- 

 sphere. In thickness and texture, both in animals 

 and vegetables, it varies exceedingly. It is very thin 

 in birds, and along the mesial abdominal line of fish. 

 In some animals, however, as the elephant and 

 rhinoceros, it is so thick and impenetrable, that it 

 constitutes an urmour of defence which resists the 

 assault of arrows, swords, javelins, and even musket- 

 balls. It is thinnest in the human body around the 

 lips, at the tip of the tongue, and at the extremities of 

 the ringers ; hence the sense of touch is most ex- 

 quisite in these parts. It is thickest in the palms of 

 the hand and in the soles of the feet, where, from 

 repeated pressure, it is often converted into a dense 

 horny substance. This thickness, however, is not 

 altogether the result of pressure ; for, even in the 

 new-born infant, the cuticle in the palms of the hands 

 and the soles of the feet is thicker than in any other 

 part of the body. Its thickness, in like manner, 

 varies in different plants. In the leaves of the pearly 

 aloe it is very thin and delicate ; around the trunk of 

 the plane-tree very thick and coarse. Although 

 insensible, this integument is still to be regarded as 

 a part of the living system, for it is constantly under- 

 going decay and renovation. From the human body 

 it continually exfoliates in small scales, and in some 

 persons in very large patches, especially after sick- 

 ness, on account of the vessels, which may be 

 regarded as the connecting link between it and the 

 subjacent layer, having become debilitated. At 

 certain seasons of the year some animals, as serpents 

 and caterpillars, cast their skin in an entire sheath. 

 It is the same with plants. From the birch and 

 currant tree the cuticle peals off constantly in small 

 scales ; from the elm it is detached in large flakes. 

 The connexion between the cuticle and the subjacent 

 layer of skin is very close ; it is, however, readily 



separated by blisters and by heat. Alcohol alflo 

 loosens it in many of the inferior animals, as may bo 

 observed by immersing worms in this liquid. When 

 the cuticle of the blistered surface has been thus 

 destroyed, it is very speedily renewed more speedily, 

 indeed, than any other tissue of the body. 



The skin, being the outer covering of the body, 

 and affording it a surface of protection, does not 

 readily absorb extraneous matters ; yet, when the 

 epidermis or cuticle is removed, and the subjacent 

 layer laid bare, then absorption takes .place very 

 rapidly ; hence, in order that the operation of 

 inoculation or vaccination shall take effect, the virus 

 must be introducod below the cuticle. This has 

 been a subject of some contention ; for, although the 

 cuticle does obviously permit the trausudation of 

 sensible perspiration, the pores through which it 

 passes are certainly not perceptible. The fact of cuti- 

 cular absorption (says Dr. Milligan, after reviewing 

 the experiments of many philosophers) may be thus 

 stated : The cuticle has no absorbing orifices open- 

 ing on its surface, and the substances supposed to be 

 taken up by these really make their way into the 

 body by the action of the absorbing vessels of the 

 lungs and subjacent cutis vera; yet, from the imbib- 

 ing faculty common to the cuticle with dead or unor- 

 ganised matter, many substances may, by long macer- 

 ation or exiernal violence, find a passage through it 

 without any laceration being visible. It may be pro- 

 per, however, to observe, that pores running in a 

 spiral direction have been discovered in the cuticle of 

 the whale ; and, arguing from analogy, it may perhaps 

 be inferred that similar spiral pores exist in the 

 human cuticle, although so minute as to escape 

 demonstration. The eminent Amici has, by the aid 

 of his powerful microscope, shown that oval orifices, 

 or stomata, as they are called, exist in the cuticle of 

 plants, especially of those which have a green colour. 

 No such stomata have, however, been detected in 

 aquatic plants ; their use, it is presumed, is to exhale 

 water and absorb air. There are many provisions in 

 animals to preserve the cuticle in a healthy state, 

 which consist principally in secretions of an* oily or 

 viscid nature. In fish and mollusca it is defended 

 from the action of the water by a viscid or glutinous 

 secretion, which is continually poured out on the 

 surface. This secretion keeps the skin of whales soft 

 and smooth, like oiled silk, and enables them and 

 other aquatic animals to emerge from the water with 

 the cuticle dry. It is in some cases glairy and 

 adhesive, as in the common slug ; or mucous and 

 slippery, as in the common eel. The cuticle of 

 animals is, in the living body, readily distended, as 

 may be observed by its extension in tumours, or 

 swellings of subjacent parts. It is, however, less 

 elastic in plants. When overtight, it causes contrac- 

 tion of the stem, as may be often seen in the plum or 

 cherry-tree ; and when subjected to pressure from 

 unnatural excrescences, it is frequently ruptured ; so 

 also, when the trunk of a tree, as the oak or the elm, 

 has attained a certain size, the surrounding cuticle 

 cracks, and the surface of the trunk becomes rugous. 

 Immediately below the cuticle, and intermediate be- 

 tween it and the cutis vera, is the second layer of the 

 skin, which was supposed by Malpighi to be formed 

 of a peculiar mucus, wherefore it was called the 

 RETE, or CORPUS MUCOSUM. Other authors regard 

 it as a vascular net-work ; and M. Gall supposed that, 

 it consists of matter similar to the brown matter which 



