Excerpt from Mechanical Principle in the Circulation in the Embryo, Placental Souffle the Analogue of Respiration: Respiration in the New-Born, the Change in Mechanics Which This Involves; Incubation, the Relation This Sustains to the Air-Chamber in the Egg; Mode of Grafting the Ovum in the Tissues of the Womb
Thus, in the case of the placental soufﬂe it is 30 to 35, and in the foetal heart the pulsations are from 120 to 140 per minute; while, in the case of the air breather, the pumping action in the trunk or respiration is from 16 to 20, and in the heart from 60 to 80 per minute. Again, this action in the placenta serves not only to pump the ﬂuids in and out of the sinuses, but at the same time it also aspirates the venous blood in the embryo for effecting oxygenation in it the same as 'obtains in the lungs the heart and vessels assisting in the one as well as in the other, since it all forms a connected movement. We now see that by reason of the great increase in pressure that obtains in the embryo, the action in the organs for changing pressure is materially assisted, since the ﬂuids ﬂow more readily in consequence. And here comes in the benefit of the amniotic ﬂuid, which not only increases pressure in proportion, but at the same time it serves to transmit the force in the placenta and uterine walls to the embryo for compelling corresponding changes in pressure upon the blood in con nection with the special functions.
As illustrating this fact, we see that when the placenta expands for aspirating the ﬂuids in the uterine sinuses, the organ advances into the uterine cavity, it swells out and occupies more room, and, by thus encroaching upon the embryonic area, it produces corresponding increase in pressure upon the liquor amnii and embryo, with low pressure in itself, which fulfils the conditions for increasing cir culation from the embryo to the placenta, at the same time, that it should aspi rate the ﬂuid in the uterine sinuses. It could not do otherwise in the very nature of things. During contraction in the placenta, the opposite conditions should obtain, since this would determine high pressure in the latter with low pressure in the embryo, the blood in consequence ﬂowing through the umbilical vein with augmented speed, and for the reason that contraction should reduce the volume of the placenta, which would inevitably reduce pressure in the embryo in proportion, the blood ﬂowing from one into the other in conformity with organic law. To this, again, must be added the action in the heart for aspirating the blood in the placenta. The media in which the animal lives obviates the necessity for the extensive arrange ments for reducing pressure in the chest, which obtain in the lighter media of the atmosphere, the heart, together with the iorce in the placenta and umbilical vein, sufficient for the purposc.
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