. IV. TJRANFORMATIONS EFFECTED. 91 



constantly passing out, or exhaling. The portion which 

 escapes varies according to the nature of the liquid ; that 

 is to say, according to the greater or less facility with 

 which it is imbibed by the tissue of the vessel. In pro- 

 portion as the sides of this vessel are externally more or 

 less moist, so will the internal liquid flow out with more or 

 less difficulty. The exhalation will be augmented if, in 

 consequence of the very large quantity of contained liquid, 

 the walls of the vessel are subjected to increased pressure. 

 All these particularities of exhalation, which result from 

 whafrwe regarded simply as a physical phenomenon, and 

 which depend on the same principles as absorption, are de- 

 monstrated by experimental physiology. 



Edwards has proved, that cutaneous exhalations is, in 

 some cases, ten times greater in dry than in moist air, and 

 that it is doubled in passing from to -f 20 centig. 

 [= 32 Fahr. to 68.] He also found that transpiration was 

 augmented by agitating the atmospheric air around the 

 body of the animal. These results are evidently the very 

 natural consequences of physical principles, too well known 

 to be repeated here. 



Transformations effected by Absorption and Exhalation. 

 Some of the phenomena of absorption and exhalation in 

 living beings, are accomplished by the transformation of 

 the absorbed or exhaled body. The liquid which is imbibed 

 by a membrane, and exhaled from its opposite surface, is 

 not identical with that which was placed in contact with 

 the absorbing membrane. This happens in most of the 

 cases of exhalation, and principally in the secretions. 



We are very far from expecting to find, in the present 

 condition of physico-chemical knowledge, an explanation 

 of the phenomena of the secretions. We must admit that 

 they form as yet one of the most obscure subjects of the 

 animal economy. With respect to exhalation it may be 



