OF THE ANIMAL FRAME. 



125 



than in the front of the body ; but in the different classes or genera of ani- 

 mals it offers us every possible variety. Generally speaking, it is thinnest 

 in birds., excepting in the duck tribe and in birds of prey. Its consistency 

 and elasticity in horses, oxen, sheep, and other cattle, render it an object 

 of high yalue, and lay a foundation for a variety of our most important 

 trades and manufactures. In many animals it is so thick and tough, as to 

 be proof against a musket-ball. It is sometimes found so in the elk, but 

 usually so in the elephant, which, at the same time, possesses the singularity 

 of being sensible to the sting of flies. The skin of the rhinoceros despises 

 equally the assault of swords, musket-balls, and arrows. 



I have observed already, that in many animals the skin performs the 

 office of a muscle, though it is seldom that any thing like a fibrous struc- 

 ture can be traced in it. The skin of man offers a few partial instances of 

 this power, as in the forehead and about the neck. In most quadrupeds 

 we trace the power extending over the whole body, and enabling them to 

 throw off at their option insects and other small animals that irritate them. 

 The skin of the horse shudders through every point of it at the sound of a 

 whip, and is said to be generally convulsed on the appearance of a lion or 

 tiger. Birds, and especially the cockatoo and heron tribes, derive hence 

 a power of moving at pleasure the feathers of the crest, neck, and tail ; 

 and the hedgehog, of rolling himself into a ball, and erecting his bristles 

 by way of defence. 



The colour of the skin is derived from the rete mucosum, or mucous 

 WEB, which, as 1 have already remarked, is disposed between the true skin 

 and the cuticle. The name of rete, or web, however, does not properly 

 apply to this substance, for it has no vascularity, and is a mere butter-like 

 material, which, when black, has a near resemblance in colour, as well as 

 consistency, to the grease introduced between the nave of a wheel and its 

 axletree. It is to this we owe the beautiful red or violet that tinges the 

 nose and hind-quarters of some baboons, and the exquisite silver that 

 whitens the belly of the dolphin and other cetaceous fishes. In the toes 

 and tarsel membrane of ravens and turkeys it is frequently black ; in hares 

 and peacocks, gray ; blue in the titmouse ; green in the water-hen ; yellow 

 in the eagle ; orange in the stork ; and red in some species of scolopax or 

 woodcock. It gives that intermixture of colours which besprinkles the 

 skin of the frog and salamander ; but it is for the gay and glittering scales 

 of fishes, the splendid metallic shells of beetles, and the gaudy eye-spots 

 that bedrop the wings of the butterfly, that nature reserves the utmost 

 force of this wonderful pigment, and sports with it in her happiest caprices. 



The different colours, and shades of colours, of the human skin, are 

 attributable to the same material. Most of these, however, are intimately 

 connected with a very full access of solar light and heat ; for a deep sun- 

 burnt skin'has a near approach to a mulatto,* And hence the darkness 

 or blackness of the compU -^lion has been generally supposed to proceed 

 from the effect produced upon the mucous pigment by the solar rays^ and 

 especially those of the calorific kind, in consequence of their attracting and 

 detaching the oxygene of the pigment in proportion to the abundance with 

 which it impinges against the animal surflice, and, in the same proportion, 

 setting at liberty the carbone, which is thus converted into a more or less 

 perfect charcoal. As this, however, is a subject which I shall have occa- 



* Humboldt, Essai Polit, snr la Noiivelle Espagne, &c. 



