96. Some have thought that the amnionic fluid was absorbed through the pores of the skin (Osiander), others through the mammæ of the fœtus (Oken). That the vesicula intestinalis (umbilicalis) contributes to the growth of the embryo is a great deal more probable (Blumenbach, Sœmmering, Lobstein, Joerg.) It is also not improbable that the gelatine of Wharton, contributes to that object (Lobstein). But these are all conjectures, for the probability or improbability of which as many arguments and real facts have been alleged on equally unquestionable authority. “Ce sujet,” observes Magendie, “a souvent exercé l’imagination des physiologistes, sans aucun profit réel pour la science.” 97. I am more inclined to believe in the existence of respiration in the fœtus as an additional means of facilitating growth and entertaining inherent life (Geoffroy St. Hilaire, Müller). The presence of air, analogous to atmospheric air, in the amnionic fluid, has been detected (Lassaigne). I once had in my possession an intact ovum at five months (30th June, 1826,) which served me for the purpose of studying more particularly the real structure of the placenta, and which contained, besides the amnionic fluid, a bubble of air about the size of a small plumb. Only a portion of this was, through the awkwardness of my assistant, received in a glass tube containing distilled water, while I punctured, under water, the membranes in the centre of the bubble. This portion was afterwards made to pass through a saturated solution of lime in water, and produced a visible cloudiness denoting the presence of carbonic acid. The respiration of the fœtus is supposed to be effected by the cutaneous pores, as in aquatic insects (Geoffroy St. Hilaire). In addition to which the placenta is looked upon as performing the office of lungs (Müller). Dr. Edwards’s experiments on the asphyxia of the _Batraciens_, may serve to throw light upon this question (Breschet). 98. The nature of the changes which the blood in the fœtus may be supposed to undergo from arterial to venous, and the converse, has not been satisfactorily ascertained. The colour of the blood in the umbilical vein is something lighter than that in the umbilical arteries (Mayo). This alleged change is not admitted by others (Meckel). I have never been able to detect the least difference between the arterio-umbilical and venous-umbilical blood, in the many cases I have examined. But the absence of any change of colour does not necessarily imply the absence of any inherent change in the blood of the two systems. The globules of the fœtal blood do not resemble those of the blood of the mother (Experiments alluded to by Dr. Breschet).