2-20 



CUTANEOUS SYSTEM. 



exists in the brain. It may be described as a thin 

 extended puJpy layer. It is the seat of colour, being 

 white in the European, copper-coloured in the 

 American, and black in the negro. Haller, Camper, 

 and Blumenbach, doubted its existence in very fair 

 persons. It is certainly not seen distinctly excepting 

 in the negro. 



The different complexion or colour of mankind, in 

 different regions of the globe, has, it is notorious, 

 given rise to various opinions and speculations ; by 

 some, being referred to a difference in original or- 

 ganisation ; by others, being ascribed to the influence 

 of climate, food, and other secondary causes. That 

 this rete mucosum is, however, really the seat of 

 colour, there appears to be no doubt ; and the 

 following ingenious theory in explanation has been 

 proposed by Blumenbach : The human body, it is 

 well known, throws off a vast quantity of carbonic 

 acid ; that is, carbon in combination with oxygen gas. 

 He supposes, then, that this carbonic acid is in this 

 mucous layer decomposed, the oxygen is set free, 

 and the carbon or colouring matter deposited on the 

 mucus, which combines with it. This decomposition 

 is presumed to be determined by the intense light 

 and heat of a tropical climate ; those parts of the 

 body, therefore, which are protected from the light 

 and heat of the sun, are not so dark as those which 

 are more exposed. The palms of the hand, and the 

 soles of the feet, are not in the negro so black as the 

 face, neck, and back of the hand. African ladies, 

 who live in the shade, have a much paler complexion 

 than those who are much occupied in the open fields. 

 It is darker in some parts of the body than in others, 

 as in the eyelids and arm-pits. According to Cuvier, 

 the shell of molluscous animals, the crust of the 

 lobster, and other Crustacea, occupy the place of this 

 layer. It also degenerates into the thick dense 

 horny substance, which form the beaks and claws of 

 birds, and the claws of other animals. Under the 

 cuticle of plants, the corpus mucosum is also found, 

 and is described as the cellular integument (envelope 

 ccllulaire). 



It is very obvious, in mosses and ferns, and is in 

 plants also the seat of colour, being green in young 

 stems, and white in those which are colourless. 

 Mirbel remarks, that leaves consist almost entirely of 

 this substance, covered on each side with cuticle. 

 The stems and branches of both annual and perennial 

 plants are invested with it ; but in woody parts it is 

 dried up and re-produced continually, such parts only 

 having that reproductive power. The old layers 

 remain, are pushed outwards by the new ones, and 

 form at length the rugged dry dead covering of the 

 old trunks of trees. In the Quercus suber, a species 

 of oak abounding in dry mountainous districts in the 

 south of France, and in Spain, Portugal, Italy, and 

 Barbary, this herbaceous envelope is remarkably 

 thick, light, and .porous, and constitutes what is well 

 known as the cork of commerce, a substance which was 

 well known to the Greeks and Romans, who used it as 

 stoppers for vessels (Pliny,Hist. Nat., lib. xvi. cap. 8.), 

 although it was not extensively applied to this pur- 

 pose until glass-bottles were introduced, which was 

 generally done in the fifteenth century. In this part 

 of the plant the principal changes of the sap take 

 place, and an operation is effected which is of vast 

 importance in the economy of nature. Already it 

 has been stated, that the human body throws off 

 continually a certain quantity of carbonic acid gas ; 



by the respiration alone about a pound of carbon is 

 got rid of daily ; mammalia, and inferior animate, 

 likewise expire it ; as do also plants when in the 

 shade. This being a very noxious, indeed poisonous 

 gas, it may reasonably be asked, how the atmosphere 

 is purified from it, and the earth rendered fit for the 

 abode of living beings ? Herein the wisdom of 

 creative Providence is beautifully illustrated. Car- 

 bonic acid is composed, it has been said, of carbon 

 and oxygen ; the carbon is the basis of vegetable 

 bodies, the characteristic ingredient of all kinds of 

 charcoal. When the sun shines upon a plant, its 

 leaves absorb the carbonic acid from the atmosphere, 

 and decompose it ; and this takes place in the herba- 

 ceous envelope ; here the oxygen is set free, and the 

 carbon left to be appropriated to the basis of the 

 plant. The vegetable creation, therefore, is con- 

 stantly purifying the atmosphere, yielding for every 

 volume of carbonic acid which it absorbs an equal 

 volume of pure oxygen. Upon this principle, some 

 have supposed that, in the beginning of the world, 

 plants were created before animals, and gradually 

 purified the atmosphere, so as to render it fit for their 

 abode. Be this as it may, the provision is exceed- 

 ingly interesting, and calculated to excite the admi- 

 ration of every reflecting mind. 



Underneath this mucous layer, or rete mucosum, is 

 the cutis vera, or true skin, which exists in all animals; 

 but is less distinct in mollusca and Crustacea. In 

 quadrupeds it appears to consist of solid fibres, which 

 cross each other in every direction ; in fish it seems 

 an homogenous and continuous membrane. Over this 

 integument, an infinite number of blood vessels, and 

 the extremities of nerves are distributed ; so that it is 

 properly speaking, the seat of the sense of touch. It 

 is provided also with a vast number of little eminences 

 or papillae, which were discovered by Malpighi in the 

 foot of a pig, in each of which the extremity of a nerve 

 is supposed to terminate. These papillae are particu- 

 larly conspicuous in the parts most appropriated to 

 the sense of touch ; as the tips of the fingers, the point 

 of the tongue, and the lips. They are also well seen 

 in the bills of aquatic birds, as the swan, goose, and 

 duck, and doubtless enable these birds to find the 

 food concealed in the mud. They are also larger 

 upon the lips of fish ; on the toes of birds which, like 

 those of the parrot kind, use their feet as organs of 

 prehension; and round the lips of the shrew, the mole, 

 and animals that burrow under ground. The vessels 

 of this true skin throw off the watery part of the bloou 

 in the form of insensible and sensible perspiration ; 

 the former escapes imperceptibly, the latter percep- 

 tibly. By some it is considered doubtful whether the 

 vessels of insensible are the same as those of sensible 

 perspiration ; the fact that the dog perspires insen- 

 sibly, but does not perceptibly, favours the idea of the 

 two kinds of perspiration being dependent on a dif- 

 ferent set of vessels. The cutaneous perspiration serves 

 several important purposes in the animal economy ; it 

 keeps the outer skin or cuticle moist and supple ; it 

 favours the exercise of taste and touch ; and regulates 

 by its evaporation the temperature of the body. The 

 cutis vera is also supplied with a number of little 

 organs called follicles, which secrete an unctuous and 

 sometimes sebaceous matter, varying in consistence, 

 odour, and other qualities in different animals, arid 

 which, as already premised, preserve the skin in a 

 healthy state. The vessels also of the true skin secrete 

 carbonic acid, which is discharged from the surface of 



