CIRCULATION OF THE FCETUS. 225 



sions the formation therein of an abundant quantity of mucus that 

 the foetus digests, and on which it grows. Finally, Dr Lee of Lon- 

 don has just performed some new experiments, whence it results that 

 the use of the liver is to secrete an abundant albuminous and nutri- 

 tive matter; that this substance fills the hepatic ducts, the duodenum 

 and small intestines; while in the stomach we find only an acid fluid, 

 and meconium in the large intestines. 



577. Of these different uses, not one is matter of demonstration; 

 those indicated by Fourcroy, M. Lobstem and M. Geoff"roy, are even 

 based upon mere suppositions, that are easy to overthrow; and 

 although the theory of Dr Lee and Dr Front is supported by some 

 facts, it seems to be the dictate of prudence that we should wait 

 before we decide, and admit that at present we do not know what 

 influence is exerted by the liver on the foetal blood. 



§. III. Of the Respiration of the FcBtiis. 



578. Air being indispensable to respiration, it seems quite natural 

 that that function should have no existence in the foetus; but on the 

 other hand, as absorption of air or oxygen seems to be indispensable 

 to the maintenance of life in all organic beings, attempts have been 

 frequently made to prove that all animals respire during their foetal life. 



571). As to the human species, it has been said that the placenta 

 receives oxygen from the blood of the mother at the same time that 

 its own parts with certain heterogeneous principles, as, for example, 

 a portion of its serum: this opinion, which is of an ancient date, has 

 been latterly defended by MM. Lobstein, Meckel, and Muller. 



It is true, that in order to explain the changes undergone by the 

 blood in passing through the placenta, we may compare that work 

 to respiration, but to accept such a comparison in the very letter, 

 would be most strangely to wrest the analogies. The blood which 

 re-enters the umbilical vein is doubtless modified, but it is not red- 

 der than it is in the arteries; the change it has just experienced 

 does not therefore in the least resemble that which occurs in its 

 passage from the pulmonary arteries into the pulmonary veins of the 

 adult. 



580. Some other persons, and particularly M. Geofl'roy de Saint 

 Hilaire, have admitted that the foetus absorbs air or a vivifying gas 

 from the whole surface of its body, by a kind of trachge like tliose 

 of insects, or even by the pulmonary passages, which might in such 

 case be compared to branchiae, and that it respires after the manner 

 of fishes; but I have already stated that the gas obtained by M. Las- 

 saigne in his first experiments was only a compound of carbonic acid 

 and azote. 



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