554 ABSORPTION BY THE SKIN. [Book n. 



by abraded surfaces where the dermis is laid bare or covered 

 only by the lowest layers of epidermis, but it has been debated 

 whether substances in aqueous solution can be absorbed by the 

 skin when the epidermis- is intact, the evidence on this point 

 being contradictory. In the case of the skin of the frog an 

 absorption of water 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 com- 

 mon experience seems to shew that it does. Nevertheless the 

 results of actual experiment are conflicting. Some observers 

 maintain that soluble non-volatile substances are not absorbed, 

 and that volatile substances such as iodine which may be de- 

 tected 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 volatili- 

 zation 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 condi- 

 tions 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, espe- 

 cially 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. 



