the Question I find this Great Man to have slipt into. For he thinks, that a Fœtus is sooner suffocated after having once breath'd, than if it had not breath'd at all, and that by breathing it had contracted something which render'd it more perishable. Idem tamen secundis exutus, (says he) si semel aerem intra Pulmones attraxerit, postea ne momentum quidem temporis absque eo durare possit, sed confestim moriatur. And presently after, Siquidem constat, fœtum, postquam eum semel hauserit, citius suffocari; quam cum ab illo prorsus accebatur. The Doctor observing a Fœtus to live longer without Respiration, and to dispence better with the want of Air while included in the Membranes intire, than it cou'd afterwards; infers thence, that the Air does in the first Act of Inspiration impress upon the Lungs some quality, which renders it ever after more indispensably necessary. But allowing his Observation, I must yet deny his Inference to be good: For deprive a Fœtus of means of respiring, and then take it out of the Membranes, and it shall be as soon suffocated, as if it had respired before. This proves, that this necessity of intercourse with the Air, by way of the Lungs, is not the Offspring, but the Parent of Respiration, and that, that Learned Man was drawn into a Fallacy of Non causa pro causa.
The Reason of this Necessity is the pressure of the External Air upon the Surface of the Body, from which it was defended by the Interposition of the Membranes, and the Humours contain'd, which are not so compressible as the Body of the Fœtus it self. So soon therefore as the Fœtus is excluded, and expos'd to the immediate contact of the ambient Atmosphere, the Vessels and all the Cavities of the Body must necessarily be so compress'd, that the Fluids can't have room for motion, and consequently the Fœtus could have no Life, if Nature had not contriv'd by the motion of the Thorax to remove and admit that pressure alternately, and thereby to