352 HANDBOOK OF PHYSIOLOGY: 



cord and may be reflexly as well as directly excited. The nerve-fibres 

 which induce sweating may act independently of the vaso-motor fibres, 

 whether vaso-dilator or vaso-constrictor. This will explain the fact that 

 sweat occurs not only when the skin is red, but also when it is pale, and 

 the cutaneous circulation languid, as in the sweat which accompanies 

 syncope or fainting, or which immediately precedes death. 



(5.) The Skin has a farther function, that of Absorption. 

 Absorption by the skin has been already mentioned, as an instance in 

 which that process is most actively accomplished. Metallic preparations 

 rubbed into the skin have the same action as when given internally^ 

 only in a less degree. Mercury applied in this manner exerts its specific 

 influence upon syphilis, and excites salivation ; potassio-tartrate of anti- 

 mony may excite vomiting, or an eruption extending over the whole 

 body ; and arsenic may produce poisonous effects. Vegetable matters, 

 also, if soluble, or already in solution, give rise to their peculiar effects, 

 as cathartics, narcotics, and the like, when rubbed into the skin. The 

 effect of rubbing is probably to convey the particles of the matter into 

 the orifices of the glands whence they are more readily absorbed than 

 they would be through the epidermis. When simply left in contact 

 with the skin, substances, unless in a fluid state, are seldom absorbed. 



It has long been a contested question whether the skin covered with the 

 epidermis has the power of absorbing water ; and it is a point the more 

 difficult to determine because the skin loses water by evaporation. But, 

 from the result of many experiments, it may now be regarded as a well- 

 ascertained fact that such absorption really occurs. The absorption of 

 water by the surface of the body may take place in the lower animals 

 very rapidly. Not only frogs, which have a thin skin, but lizards, in 

 ivhich the cuticle is thicker than in man, after having lost weight by 

 being kept for some time in a dry atmosphere, are found to recover both 

 iheir weight and plumpness very rapidly when immersed in water. 

 When merely the tail, posterior extremities, and posterior part of the 

 body of the lizard are immersed, the water absorbed is' distributed 

 throughout the system. And a like absorption through the skin, though 

 to a less extent, may take place also in man. 



In severe cases of dysphagia, when not even fluids can be taken into 

 the stomach, immersion in a bath of warm water or of milk and water 

 may assuage the thirst; and it has been found in such cases that the 

 weight of the body is increased by the immersion. Sailors also, when 

 destitute of fresh water, find their urgent thirst allayed by soaking their 

 clothes in salt water, and wearing them in that state; but these effects 

 are in parb due to the hindrance to the evaporation of water from the 

 .skin. 



(6.) For an account of the important function of the skin in the 

 regulation of temperature, see Chapter on Animal Heat. 



