STRUCTURE OE THE HUMAN BODY. 35 



cases, is generally of a bright rose-colour, and the eyes are 

 so sensible to light, that they cannot be kept open in the 

 sun-shine, although in the shade, or dusk of the evening, the 

 vision is perfect. It is now well ascertained that the red- 

 ness of the eye and the whiteness of the skin in albinos 

 depends on the same physical defect in their organization, 

 and that it is owing to the absence of the colouring mat- 

 ter in the rete mucosum. In the eye, this matter, spread 

 over the retina, is called Pigmentum nigrum, or the black 

 paint. 



24. What is called thefCorpus papillarej is merely a col- 

 lection of small papillae, formed by the extremities of nerves 

 and blood-vessels, and lying immediately under the mucous 

 web, &c. It is|m this layer that the sense of touch resides ; 

 the papillae can easily be seen when the cuticle has been 

 removed by a blister. 



25. The Cutis vera, or true sldn, is the innermost of the 

 four layers above mentioned, flt is a firm stratum of dense 

 fibres intersecting each other in every direction, and having 

 holes for the passage of vessels and nerves^ 



26. The true skin is composed chiefly of gelatine, and hence 

 is ijsed for the manufacture of glue^ Gelatine combined 

 with tannin, which is a proximate vegetable principle ob- 

 tained from oak and other barks, forms a compound that is 

 insoluble in water ; and it is to this circumstance that 

 leather owes the properties it possesses. Leather, then, may 

 be considered as the product of the union of tannin and 

 gelatine. 



27. Though the skin consists of four distinct strata, yet 

 it is only^rom one-sixth to one-fourth of an inch in diameter. 

 The true skin is united to the structure below by cellular 

 membrane, and this, with the layers above described, consti- 

 tute the common integument. The following sketch repre- 

 sents the several layers entering into the composition of the 

 skin. 



