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6. There is only one experiment which can apply to this ques- 

 tion; it is by observing whether chyle, thrown into the vessels of the 

 lungs, is made blood. Thus far the experiment is practicable: but 

 but there would be absurdity in attempting it, 1st, because in the 

 Jiving organs the blood in the pulmonary vessels would be fluid, the 

 chyle would mix with this blood, and the design of the experiment 

 would thus be frustrated; 2nd, because if the blood were not fluid, or 

 if it were in part coagulated, then chyle would in some degree mix 

 with it, and receive a tiage from its colouring matter; and, 3rd, because 

 the lung in this state would be deprived of its life; a circumstance 

 sufficiently important to invalidate any inference which might be 

 founded upon an assumed analogy between the natural and the 

 artificial process. 



7. We are then, it appears, furnished with no proofs, either 

 natural or from the resources of art, by which the seat of the con- 

 version of chyle into blood may be shewn to be in the lungs. As 

 we cannot obtain proofs with respect to this conversion, we must 

 seek for evidence of a weaker kind. 



8. The conversion takes place somewhere in the sanguiferous 

 system : is it by a property possessed by the blood-vessels them- 

 selves? There is, it must be replied again, no proof of the existence 

 of such a property; neither is there any experiment which would 

 decide the question, unless it be one by which the mixture of chyle 

 with ready formed blood would be prevented. This may be done 

 by enclosing a certain space of an artery of a living subject between 

 two ligatures, and injecting this portion with chyle; but if the con- 

 version did not occur in this space, it could scarcely, on this account, 

 be inferred that the arteries do not possess the properties by which 

 the conversion is effected, as the action of the ligatures may intercept 

 a spiritual intercourse, upon which such a function may depend. 

 However, the evidence furnished by the result of such an experi- 

 ment is liable only to the general objection that the natural function 

 of a part is to be inferred suspiciously from experiments which place 

 it in a preternatural condition, and thereby destroy the analogy upon 

 which the inference is founded. This latter is the point to be attend- 

 ed to in experimenting: and, in the present case, to decide whether 

 the operation of the ligatures interfere with those points of analogy 

 which affect the inference, would require another investigation. 



9. There is only one obvious change which takes place in the 

 lungs, and that is the conversion of venous into arterial blood. 

 This change appears to be wholly atmospherical, as a similar one is 

 found to occur in venous blood, when exposed to the air, removed 

 from any influence of the properties of the living structures. This 

 is a change upon which chyraistry has been busily employed ; and, 

 as is usual with chymical investigations, applied to animal pheno- 

 mena, just so much has been ascertained as is not worth knowing. 



. 10. The seats of the other conversions of the circulating fluids 

 may be fixed with some precision, because it may he observed 

 where, in what order of vessels, in what viscus, these changes occur. 



