Bauhaus-Universität Weimar

OTHER INVOLUNTARY MOTIONS. 119 
the lungs ; and becaufe its fluids, being derived from the blood of 
the mother, which has fuftained the aétion of the air in her lungs, 
muft be equally fit for its nouriihment and fupport as for hers. 
When the fœtus, after being feparated from its mother, remains in 
its fecundines, it lives for a confiderable time without breathing ; 
becaufe the circulation of the blood continuing in the fame man¬ 
ner as when it was in the womb, only a fmall portion of it pafles 
through the lungs. 
After birth, when the fœtus has once been accuflomed to breathe, 
it foon dies, if refpiration be difcontinued * j becaufe the blood, 
which formerly went by the foramen ovale and duHus arteriofus, 
pafles now through the veflels of the inflated lungs ; and although 
we cannot fuppofe thefe paflages to be inftantly fhut after breath¬ 
ing begins, yet as the veficles of the lungs, after having been once 
inflated, never collapfe fo far as to occupy as little fpace as be¬ 
fore, their veflels muft go on to receive a greater quantity of blood 
than before birth, and confequently to tranfmit this fluid in greater 
abundance to the left finus venofus ; by which means the paflage of 
the blood into this finus, by the foramen ovale, will, in a great mea- 
fure, be prevented ; at the fame time, by the inflation of the lungs, 
the pulmonary artery will be raifed, and the fituation of the duftus 
arteriofus fo changed, as to render the paflage of the blood through 
it lefs favourable. Further, after birth, when the umbilical arteries 
are tied, the blood pafling through the duftus arteriofus into the a- 
orta will meet with greater refiflance than formerly ; fince the fluids 
pufhed into this artery by the two ventricles of the heart, will find 
a lefs ready paflage, as a confiderable part of the veflels through 
which they ufed to flow are thus obftructed. 
Hence, if refpiration be once begun, though performed but for 
a fhort time, the blood, notwithftanding its being afterwards re- 
ftrained 
* M. de Haller (a) has well obferved, that notwithftanding Harvey’s words may feem to in- 
finuate that * fœtus which has once breathed, inftantly dies after this atfion is interrupted • yet 
fœtufis which have breathed only for a fhort time, can live feveral minutes without refpira¬ 
tion. 
(3) Elemcat, Phyfiolog, tom, 3,
        

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