456 AESOEPTION. 



have seen how admirably the respiratory surface is calculated 

 for the introduction of gaseous principles into the blood. 1 

 The great rapidity with which the oxygen of the inspired 

 air penetrates through the delicate covering of the pulmo- 

 nary vessels has already been fully considered under the head 

 of Respiration. Under natural conditions, the gases of the 

 air are the only principles absorbed by the lungs ; but exam- 

 ples of the absorption of other gaseous matters are exceed- 

 ingly common, and this process has been the subject of nu- 

 merous experiments by physiologists. The fact of the ab- 

 sorption of foreign substances by the lungs, also, has long 

 been definitely settled ; but this belongs to pathology or to 

 therapeutics, rather than to physiology. 



It is now almost universally conceded that animal and 

 vegetable emanations may be taken into the blood by the 

 lungs and produce certain well-marked pathological condi- 

 tions. It is supposed that many contagious diseases are prop- 

 agated in this way, as well as some fevers and other gener- 

 al diseases which are not contagious. With regard to certain 

 poisonous gases and volatile principles, the effects of their 

 absorption by the lungs are even more striking. Carbonic 

 oxide and arseniuretted hydrogen produce death almost in- 

 stantly, even when inhaled in small quantity. The vapor of 

 pure hydrocyanic acid acts frequently with great promptness 

 through the lungs. Turpentine, iodine, and many medicinal 

 substances may be introduced with great rapidity by inhala- 

 tion of their vapors ; and we well know the serious effects 

 produced by the emanations from lead or mercury in persons 

 who work in these articles. Among the most striking proofs 

 of the absorption of vapors by the lungs are the effects 

 of the inhalation of chloroform and ether. These pass into 

 the blood and manifest their characteristic ansesthetic influ- 

 ences almost immediately. 'Not only have vapors introduced 

 in this way been recognized in the blood, but many of the 

 principles thus absorbed are excreted by the kidneys, and 



1 See vol. i., Respiration. 



