370 EXTERNAL INTEGUMENT. 



II. Phenomena of exchange effected by the skin. 



These exchanges can be effected either from without 

 inwards (absorption), or from within outwards (secre- 

 tions). 



A. Absorption. 



Absorption, by means of the cutaneous surface of the skin, 

 is still a much disputed question. One entire system (the 

 iatraliptic or endermic system) of administering medicaments 

 supposes that absorption by the skin does really take place ; 

 it must be observ.ed, however, that in such cases the condi- 

 tion of the skin is changed either by mechanical action, such 

 as mercurial friction, or by chemical action, such as the appli- 

 cation of alcoholic dyes, rancid pomades, etc. etc. Colin 

 produced absorption by mechanical action in an experiment 

 which is often referred to, and which consisted in causing 

 water impregnated with cyanide of potassium, to drip for five 

 hours upon the back of a horse ; the percussion thus pro- 

 duced at length effected the destruction of the sebaceous 

 matter, and caused the cyanide to pass into the system 

 through the skin, and the animal was poisoned by cutaneous 

 absorption. 1 The really physiological question is reduced to 

 whether a healthy skin will absorb water : the ancients main- 

 tained that it does, but our present knowledge of the subject 

 seems to show that this is a mistake. Setting aside the many 

 causes which have given rise to this error, it may be proved 

 that no absorption takes place from remaining a long time in 

 a bath : recently, at Vienna, experiments have been made of 

 long-continued immersion, as a new treatment for diseases of 

 the skin, and patients have remained immersed in a bath for 

 weeks and months, without any sensible absorption taking 

 place, the patients continuing to experience thirst, and being 

 obliged to swallow as much liquid as if they had lived en- 

 tirely in the air. . The small quantity which is occasionally 

 absorbed is either introduced by the points of transition be- 

 tween the skin and the mucous, or by the orifices of the 

 sudoriparous and sebaceous glands. It appears to be a gen- 

 eral law of animal, as well as vegetable organisms, that the 

 epidermis resists absorption : the vegetable bark, or epidermis 

 of a fruit, closely resembles the bark, or epidermis of an 

 animal ; the epidermis of a grape resists the phenomena of 



1 See G. Colin, " Physiologic comparee des Animaux Domes- 

 tiques." 1873, Vol. II. p. 123. 



