732 ABSORPTION BY THE SKIN. [BOOK n. 



and of various soluble substances certainly takes place. In the 

 case of the sound human skin there are no a priori reasons why 

 water carrying substances dissolved in it should not pass inwards 

 through the corneous as well as the other layers of the epidermis, 

 the amount so passing depending, among other things, upon the 

 condition of the skin ; and common experience seems to shew that 

 it does. Nevertheless the results of actual experiment are conflict- 

 ing. Some observers maintain that soluble non-volatile substances 

 are not absorbed, and that volatile substances such as iodine which 

 may be detected in the system after a bath containing them are 

 absorbed not by the skin but by the mucous membrane of the 

 respiratory organs, the substance making its way to the latter by 

 volatilisation from the surface of the bath. Others again have 

 found evidence of absorption, especially with volatile substances, 

 even when care has been taken to avoid all errors ; and the greater 

 weight may perhaps be given to these since they accord with 

 common experience. The conflict of experimental results, how- 

 ever, at least shews that we do not fully understand the conditions 

 under which such absorption takes place. 



There is moreover evidence that even solid particles can pass 

 through an intact skin. The lymphatics in the skin of a newborn 

 infant have been found crowded with the particles of the peculiar 

 fatty secretion which covers the skin at birth ; and solid particles 

 rubbed into even the sound skin may, especially when applied in 

 a fatty vehicle, as ex. gr. in the well-known mercury ointment, 

 find their way into the underlying lymphatics. The wandering 

 leucocytes which are at times found among the epidermic cells 

 may perhaps take part in this transport. 



