698 ABSORPTION BY THE SKIN. [BOOK n. 



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 contra- 

 dictory. 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 common 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 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 sub- 

 stances, 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, however, 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. 



