PERSPIRATION 199 



state of the blood and of the nervous system. It is estimated 

 that, as a geneKftl rule, the quantity of water excreted by 

 the skin is about double that given out by the lungs in 

 the same time. 



The amount of matter which may be lost by perspiration 

 under certain circumstftnces, is very remarkable. Heat 

 and severe labour, combined, may reduce the weight of a 

 man two or three pounds in an hour, by means of the 

 cutaneous perspiration alone ; and there is some reason 

 to believe that the total amount of solids which 

 are eliminated by profuse sweating may be consider- 

 able. 



9. A Comparison of the Lungs, Kidneys, and 

 Skin. — It will now be instructive to compare together in 

 more detail than has been done in the first Lesson (p. 24), 

 the three great organs — lungs, kidneys, and skin — which 

 have been described. 



In ultimate anatomical analysis, each of these organs 

 consists of a moist animal membrane separating the blood 

 from the atmosphere. 



Water, carbonic acid, and solid matter pass out from 

 the blood through the animal membrane in each organ, 

 and constitute its secretion or excretion ; but the three 

 organs differ in the absolute and relative amounts of the 

 constituents the escape of which they permit. 



Taken by weight, water is the predominant excretion 

 in all three ; most solid matter is given off by the kid- 

 neys ; most gaseous matter by the lungs. 



The skin partakes of the nature of both lungs and 

 kidneys, seeing that it absorbs oxygen and exhales 

 carbonic acid and water, like the former, while it excretes 

 organic and saline matter in solution, like the latter ; but 

 the skin is more closely related to the kidneys than 

 to the lungs. Hence, as has been already said, when the 

 free action of the skin is interrupted, its work is usually 

 thrown upon the kidneys, and vice versa. In hot weather, 

 when the excretion by the skin increases, that of the 



