ORGANS OF TOUCH. 125 



matter, composed of a glandular or secreting parenchyma, situate a 

 little below the papillae, and presenting special excretory ducts, which 

 pour out the colouring matter on the surface of the derma. 



Modern observers deny, that there is any such distinct layer. Some 

 regard it as the deepest or most recently formed part of the cuticle. 

 M. Flourens 1 considers, that the term corpus mucosum ought to be re- 

 placed by that of pigmental apparatus, appareil pigmental; and that 

 the term rete or corpus reticulare in the signification of a special 

 network situate between the derma and the two cuticles, ought to be 

 banished from anatomy. The nature of the pigment will be referred 

 to hereafter, under SECRETION. 



The rete mucosum is considered to be the last formed portion of the 

 cuticle. 



3. The corpus papillare, or what M. Breschet calls the " neu- 

 rothelic or mammillary nervous apparatus,' is seated next below 

 the rete mucosum. It consists of a collection of small papillae, 

 formed by the extremities of nerves and vessels, which, after having 

 passed through the corium beneath, are grouped in small pencils or 

 villi on a spongy, erectile tissue. These pencils are disposed in pairs, 

 and, when not in action, are relaxed, but 



become erect when employed in the sense of Fi s- 42. 



touch. They are very readily seen, when the 

 cutis vera is exposed by the action of a blister; 

 and are always evident at the palmar surface 

 of the hand, and especially at the tips of the 

 fingers, where they have a concentric arrange- 

 ment. These villi are sometimes called papillse. 

 They are, in reality, prolongations of the skin ; . Papillae of the palm, the Cu- 



s * ,.1 TV/I- TTII 9i tide being detached. Magni- 



and consequently as M. Flourens 2 has re- fied 35 diameters. 



marked u the pretended corpus papillare, 



taken as a body, apart and distinct from the derma, is but an idle 



name." 



4. The corium, cutis vera, derma, true skin, is the innermost layer 

 of the skin. It consists of a collection of dense fibres, intersecting 

 each other in various directions ; and leaving between them holes for 

 the passage of vessels and nerves. It forms a firm stratum, giving 

 the -whole skin the necessary solidity for accomplishing its various 

 ends ; and consists chiefly of gelatin ; hence it is used in the manu- 

 facture of glue. Gelatin, when united with tannic acid, forms a sub- 

 stance which is insoluble in water ; and it is to this combination that 

 leather owes the properties it possesses. The hide is first macerated 

 in lime-water to remove the cuticle and hairs, and leave the corium or 

 gelatin. This is then placed in an infusion of oak bark, which con- 

 tains tannic acid. The tannic acid and the skin unite ; and leather is 

 the product. 



These four strata constitute the skin, as it is commonly called; yet 

 all are comprised in the thickness of two or three lines. The cutis 

 vera is united to the structures below by areolar tissue ; and this, with 



1 Op. cit., p. 38. . 2 Op. cit., p. 38. 



