122 OF PERSPIRATION, 



All these shades of colour, as well as the other cha- 

 racteristics of nations and individuals, run so insensibly 

 into one another that all division and classification of 

 them must be more or less arbitrary. 



182. The essential cause of the colour of the Mal- 

 pighian mucus, is, if we mistake not, the proportion of 

 carbon which is excreted together with hydrogen from the 

 corium, and in dark nations, being very copious, is pre- 

 cipitated upon the mucus and combined with it.* 



183. The corium, which is covered by the reticulum 

 and epidermis, is a membrane, investing the whole body 

 and defining its surface; tough; very extensible; of dif- 

 ferent degrees of thickness ; every where closely united, 

 and, as it were, interwoven, with the mucous tela, espe- 

 cially externally, but more loosely on its internal sur- 

 face, in which, excepting in certain parts, we generally 

 discover fat. 



184. Besides nerves and absorbents, innumerable 

 blood vessels, of which we shall speak hereafter, pene- 

 trate to its external surface, upon which they are shewn, 

 by minute injection, (o form very close and delicate 

 net-works. 



185. A vast number of sebaceous follicles also are 

 dispersed throughout it, which diffuse over the skin an 

 oil,f thin, limpid, and not easily drying,^; altogether 



* I have given this opinion at some length in my work, De Gen. Human. 

 Varietate Nativa. p. 122 sq. ed. 3. Some eminent chemists accord with me, 

 among whom suffice it to mention the celebrated Davy, Journals of the Royal 

 Institution, vol. ii. p. 30. " In the rete mucosum of the African, the carbon 

 becomes the predominant principle ; hence the blackness of the negro." 

 W. B. Johnson, 1. c. vol. ii. p. 229. 



f- Chr. Gottl. Ludwiar, De Hi/more cittern inungentc. Lips. 1748. 4to. 



J Lyonct, Lcttre a M. Lc Cat. p. 12. 



