Bauhaus-Universität Weimar

OTHER IN VOLUNTARY MOTIONS. 43 
fer in the former than in the latter, but not that its velocity is great¬ 
er-*: and this denfity, he imagines, it acquires chiefly by being ex- 
poled to the cool air in its paflage through the Imail veflels of the 
lungs. In anfwer to which, it is fufflcient for our purpofe to ob~ 
ferve, that unlels the blood be condenled m the lungs into y of its 
former bulk, (a fuppolition which cannot be admitted), it mu A 
flow through the pulmonary vein's with a greater velocity, and 
confequently with a greater momentum, than through the two cwvte. 
The fmall expanfion and condenfation of water, oil, fpirit of wine, 
and other liquors in thermometers, arifing from conliderable degrees 
of heat and cold, fhew, that the cool air applied to the furface of 
the lungs can have but little influence in condenling the blood ; 
belides, it feems not improbable, that the blood may acquire a heat 
in the lungs fuflicient to balance the refrigeration it is there ex- 
pofed to. It is generally thought, and indeed not without good rea- 
fon, that the blood in the pulmonary veins is fomewhat denfer than 
in the correfponding artery : but this, perhaps, is not fo much to 
be afcribed to the coldnefs of the air that is infpired, as to its pref- 
fure, and to the a&ion of the elaltic veflels of the lungs. 
If it be obje&ed ta what we have offered in proof of the blood’s 
returning with greater force to the left than to the right ventricle 
of the heart, That in a fœtus in utero this feems not to be the cafe : 
it may be anfwered, That the llrength of the left ventricle in a fœtus 
exceeds that of the right but little ; or, at lealt, not near fo much as 
in adult animals : that the right ventricle not only pulhes part of 
the blood through the veflels of the lungs, but alfo diflributes a good 
deal more than ÿ of the whole mafs to the aorta and its branches: 
F 2 that 
his defcription of the lungs, or in his explanation of thofe figures. This debate might have 
been eafily decided, if the perfons concerned in it had looked into the proemium of Dr Har¬ 
vey’s book de motu cordis, &c. j where we find the following paflage ; from which it appears, 
that this fpeciality in the pulmonary veins was not unknown to that illuitrious author. 
<< Quum venam arteriofam, vas amplum magnum cum tunica arteriae fadtum, non nifi privato 
« et uni ufui, (viz. alendis pulmonibus), deliinarint : cur arteriam venalem vixpari magnitudme 
r* cum tunica venae molli, laxa, pluribus ufibus, tribus vel quatuor videlicet, fabrefaôam efle 
<( afleverant ?” 
* Mémoires de l’Acad, des fciences 1718. edit. Svo, p. 281. Szc,
        

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