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CHAP. II. The Lungs. 



], THAT the seat of the conversion of venous into 

 arterial blood is in the lungs, is very evident: it is quite another 

 matter to affirm that the lungs constitute the seat of the conversion 

 of chyle into arterial Wood. If we seek here for proofs, we shall 

 not find them. To proceed, however, 



2. Chyle, it is said, or if not said is currently imagined, is made 

 blood in the lungs. What are the grounds of the inference? Why, 

 jt will be observed, we see that the colour of the blood carried into 

 the lungs by the pulmonary artery is different from that which is re- 

 turned to the heart by the pulmonary veins. This fact relates to 

 the changes of blood, not to those of chyle. Is there no better proof! 



3. The function of the lungs, it is said, consists in an exposure 

 of blood to the influence of atmospheric air, by which it becomes 

 oxygenated. Now, then, imitate this function with respect to lacteal 

 chyle, expose it to atmospheric air, and see if it will be converted 

 into blood ; the experiment is easy. It is converted into nothing, in 

 point of colour, like blood, either arterial or venous. The lacteal 

 chyle is nearly white, its colour is not immediately changed by ex- 

 posure to air: by a continued exposure it becomes a little darker; 

 but still its colour cannot, without a great stretch of the imagina- 

 tion, be fancied to resemble distantly that of arterial blood. It re- 

 mains to be known whether any of those differences between chyle 

 and blood, which chymists have either discovered or fancied, occur 

 on the exposure of chyle to atmospherical air. 



4. From the above fact, viz. that lacteal chyle is not made 

 blood by exposure to atmospheric air, one of two inferences must 

 be deduced ; either that the conversion we are considering does not 

 take place in the lungs, or that, if it does take place in the lungs, 

 these organs possess a function independent of, or superadded to, 

 the influence by atmospherical air. These alternatives will require 

 a short discussion. 



5. We are furnished by nature with no proofs derived from the 

 observance of the phenomena of health or of those of disease, that 

 the conversion of chyle into blood takes place in the lungs. If 

 therefore we require proofs upon this point, they must be sought 

 after experimentally. 



