There are many Problems of great seeming Difficulty, the Solutions of which flow naturally from what has been laid down here: But intending to prosecute this Subject farther, and to treat of the Impediments of Respiration, and the Consequences of Respiration obstructed or intermitted, I shall reserve them for that Opportunity, and content my self here to attempt the _Harveyan_ Problem only, which has given abundance of Authors so much perplexity. That incomparable Philosopher enquires, _Why a _Fœtus_, taken out of the _Uterus_ with the _Membranes_ intire, shall live in Water some Hours without communication with the _External Air_; whereas if it be taken out and suffer'd once to breath, it can't afterwards survive a Moment without the benefit of _Respiration_._ Granting the Fact to be as he has deliver'd it, which yet is not so in all Cases, the main Difficulty is grounded on a Mistake, which from the stating of 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_.