242 FUNCTIONS OF THE SKIN. 



mersed. Gaseous substances also find entrance through the skin. If 

 the hand be put into a bell-jar containing oxygen, nitrogen, or carbonic 

 acid at the pneumatic trough, absorption of those gases ensues. Proba- 

 bly it is a standard function of the skin to permit a partial arterialization 

 of the blood, atmospheric oxygen being exchanged for carbonic acid 

 through it, an action the residual trace of the community of function be- 

 tween the skin and mucous membrane. In the case of some animals 

 this cutaneous respiration is well marked. 



Kecapitulating now the more important actions of the skin, the folio w- 

 Summarv of & statement raa 7 ^ e ma( ^ e : ^ regulates, to a certain extent, 

 the functions the amount of water in the system, disposing of it, as the case 

 of the skm. m ^ -^ e ^h er ag sensible or insensible transpiration. The 

 water doubtless maintains its liquid condition until it presents itself at 

 the mouths of the sudoriparous ducts, moistening the general surface of 

 the skin, and then being evaporated ; or, if the supply be greater than 

 can be thus removed, it accumulates as drops of sweat. There appears 

 to be no substantial reason for believing that any portion of water trans- 

 udes directly through the structure of the cuticle, since the scales' which 

 compose it are of an impervious and almost horny nature, and their in- 

 terspaces are fortified against any such leakage by the oily exudations 

 of the sebaceous glands. With the water thus presenting on the surface 

 are many compounds which are also constituents of the urinary secre- 

 tion. Among these, urea may be particularly pointed out, thus indicating 

 a similarity of instrumental action between this organ and the kidneys, 

 and this is farther substantiated by both containing provisions for the 

 elimination and escape of the hydrocarbons ; but besides these direct 

 functions there are other very important collateral agencies which the 

 skin exerts, and particularly as a regulator of temperature. In this re- 

 spect the action is, to a certain extent, meteorological. But this has been 

 previously treated of so much in detail that it is unnecessary to resume 

 the consideration of it now. 



