IMPORTANCE OF THE CUTANEOUS TRANSPIRATION. 35 



Fig. 15. evaporation tube itself, become gradually filled with brine, urine, 

 oil, &c. 



* The most general expression for these experiments and results 

 is this ; that all liquids which are in connection with a mem- 

 brane from the surface of which evaporation can take place, must 

 acquire motion towards that membrane. 



The amonnt of this motion is directly proportional to the 

 rapidity of evaporation, and consequently to the temperature and 

 hygrometric state of the atmosphere. 



That the skin of animals, and the cutaneous transpiration, as 

 well as the evaporation from the internal surface of the lungs, 

 exert an important influence on the vital processes, and thereby 

 on the state of health, has been admitted by physicians ever 



since medicine has existed; but no one has hitherto ascertained 



precisely in what way this happens.t 



From what has gone before, it can hardly be doubted, that one of the most 

 important functions of the skin consists in the share which it takes in the motion 

 and distribution of the fluids of the body 4 



The surface of the body of a number of animals consists of a covering or skin 

 permeable for liquids, from which, when, as in the case of the lung, it is in con- 

 tact with the atmosphere, an evaporation of water, according to the hygrometric 

 state and temperature of the air, constantly goes on. 



If we now keep in mind, that every part of the body has to sustain the pressure 

 of the atmosphere, and that the gaseous fluids and liquids contained in the body 

 oppose to this pressure a perfectly equal resistance, it is clear that, by the evapora- 

 tion of the skin and lungs, and in consequence of the absorbent power of the skin 

 for the liquid in contact with it, a difference in the pressure below the surface of 

 the evaporating skin occurs. The external pressure increases, and in an equal 

 degree the pressure from within towards the skin. If now the structure of the 

 cutaneous surface does not permit a diminution of its volume, a compression (in 

 consequence of the loss of liquid by evaporation,) it is obvious that an equalization 

 of this difference in pressure can only take place from within outwards ; first from 

 within, and especially from those parts which are in closest contact with the 

 atmosphere, and which offer the least resistance to the action of the external 

 pressure. || 



Hence it follows, that the fluids of the body, in consequence of the cutaneous 

 and pulmonary transpiration, acquire a motion towards the skin and lungs, which 

 must be accelerated by the circulation of the blood. 



By this evaporation, the laws of the mixture of dissimilar liquids, separated by 

 a membrane, must be essentially modified.^ The passage of the food dissolved 

 in the digestive canal, and of the lymph into the blood vessels, the expulsion of 

 the nutritive fluid out of the minuter blood vessels, the uniform distribution of 

 these fluids in the body, the absorbent power of the membranes and skins, which, 

 under the actual pressure are permeable for the liquids in contact with them, are 

 under the influence of the difference in the atmospherical pressure, which is 

 caused by the evaporation of the fluids of the skin and lungs. 



The juices and fluids of the body distribute themselves, according to the thick- 

 ness of the walls of the vessels, and their permeability for these fluids, uniformly 

 through the whole body; and the influence which a residence in dry or in moist 

 air, at great elevations or at the level of the sea, may exert on the health, in so far 

 as the evaporation may thus be accelerated or retarded, requires no special explana- 

 tion ; while on the other hand the suppression of the cutaneous transpiration must 



* Liquids move towards the membrane from which evaporation takes place, 

 f Influence of the skin and cutaneous transpiration on health. 



I The cutaneous evaporation has an important share in causing the motion of the animal fluids, 

 j Evaporation is constantly going on from the skin and lungs. 



II This evaporation must produce unequal pressure, by which the fluids acquire f ^af;Uon to- 

 wards the skin and lungs. 



fl The change of pressure influences the mixture of the fluids. 



