LECTURE V. 237 



the lungs becomes augmented in animals, 

 so are their cells minute, and the pulmo- 

 nary vessels subdivided, by which means 

 the surface of the air and the blood exposed 

 to reciprocal influence is proportionately 

 increased. Carbone is evidently thrown off, 

 and a change produced, of the precise na- 

 ture of which we are ignorant, but which is 

 rendered evident to our senses by a change 

 of colour ; for the purple current acquires 

 a scarlet hue, or, as it is commonly ex- 

 pressed, the venous blood becomes arte- 

 rious. Chemists have considered the change 

 as contributory to the production of animal 

 heat ; which opinion may indeed be true, 

 though the manner in which it produces 

 such an effect, has not as yet been explain- 

 ed." Mr. Hunter, who believed that life had 

 the power of regulating temperature, inde- 

 pendently of respiration, says nothing of 

 that process as directly contributing to 

 such an effect. He says " breathing seems 

 to render life to the blood ; and the blood 

 conveys it to every part of the body." Yet 

 he believes the blood derives vitality also 

 from the food. The experiments of Mr. 



