VOL. XXXVI.] PHILOSOPHICAL TRANSACTIONS. 36l 



Observations on a Treatise written by M. Helvetius, to prove that the Lungs do 

 not divide and expand the Blood; but that, on the contrary, they cool and 

 condense it. By F. Nicholls, F. R. S. N° 410, p. l63. 



The matter in question between Helvetius and Sig. Michelotti is, whether 

 the lungs cool and condense the blood, according to the opinion of the ancients, 

 or whether they mix, attenuate, and of consequence expand it, according to 

 the system of Dr. Pitcairn? 



The author, in order to support the opinion of the ancients, brings several 

 arguments to confute the system of Dr. Pitcairn ; the most considerable of 

 which is, that the right auricle and ventricle being considerably larger than the 

 left auricle and ventricle, and the pulmonary artery having a larger capacity than 

 all the pulmonary veins taken together, the blood must evidently occupy a 

 greater space before than after its passage througii the lungs; and because the 

 difference in the capacity of these vessels cannot be balanced by any increase of 

 the velocity, he concludes, that the blood is not attenuated and expanded, but 

 must be condensed in its passage through the lungs. And this the author 

 conceives is done by the air, which, as a fluid relatively cold, must cool and con- 

 dense the blood, to which it is so nearly applied in the action of inspiration. 



Had the author of this treatise been contented with supporting the opinion 

 of the ancients, without endeavouring to subvert the system of Dr. Pitcairn, he 

 would probably have found many advocates for his doctrine, and few opposers. 



That the blood is cooled by the action of inspiration, is a matter of which 

 Dr. N. believes few physicians doubt, when they consider that in inflammations 

 of the lungs, nothing is more earnestly desired than the breathing cool and 

 fresh air, nor does any thing more evidently conduce to the cure of these and 

 other inflammatory dispositions, than the use of fresh air. But that this is the 

 sole use of breathing, or that this cooling power can overbalance the expansion 

 from the action of expiration, is what he can nowise conceive. 



If we consider the state of the blood at its return to the heart, and how 

 careful nature has been, not to use this blood for the nourishment of the lungs 

 before it has passed through the pulmonary vein and artery, though it would in 

 that case have been as effectually cooled in the bronchial arteries as in the pul- 

 monary vessels, we are naturally led to believe, that it is some other quality 

 which has rendered it improper for nourishment, and which is to be destroyed 

 by the action of the lungs. 



For this reason, and from the structure of the parts subservient to breathing, 

 it seems evident, that the blood is mixed, attenuated, and consequently re-ex- 

 panded in the action of exspiration. Dr. N. now considers whether the action 



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