STRUCTURE OF THE SKIN. 83 



It has been supposed by some, that this layer owes it 

 colour to the action of the solar rays ; but as it is often 

 found coloured in those parts secluded from the light, into 

 which it enters along with the cuticle, such as the palate, 

 tongue and ears, we must attempt to trace its origin to 

 some other cause. BLUMENBACH refers the colour to car- 

 bon, precipitated on the mucus, and combining with it. 

 The proofs, however, are still wanting, of the presence of 

 this ingredient in the particular state of colour which char- 

 coal exhibits. Were the mucous membrane always found 

 either colourless or black, we might be induced to admit 

 the colouring matter to be charcoal ; but when this layer, 

 in different animals, exhibits all the tints of the prismatic 

 spectrum, we are inclined to reject the explanation as hy- 

 pothetical, and wait the result of more decisive experi- 

 ments. Dr BEPDOES, and afterwards FOURCROY, ascertain- 

 ed, that oxy muriatic acid deprived the skin of a negro of its 

 black colour ; but in a few days it returned with its former 

 intensity. That the colour depends on an animal oil secret- 

 ed by the true skin, is, perhaps, the most plausible conjec- 

 ture which can be advanced on the subject. 



This layer of the skin occurs not only in the warm-blood- 

 ed animals, but, perhaps, in all the inferior classes *. Cu- 

 VIER conjectures, that the shell of molluscous animals 

 and the crust of lobsters, and other Crustacea, occu- 

 py the place of this layer, as they are in immediate contact 

 with the cuticle. But as these parts are employed as or- 

 gans of protection and of support to the muscles, purposes 

 to which the mucous web is never applied in its most per- 

 fect state, analogy appears in opposition to the conjecture. 



3. Corium. This is known by the name of the cutis 



* It is necessary to add, that the existence of this layer is even denied by 

 some. Edin. Phil, Journ. i. p. 213. 



